Eoin Doyle netted twice on his Fratton return as Pompey endured a difficult afternoon on the south coast.
Both sides started the game with an attacking intent, but Oldham were in control from the moment they grabbed their early opener.
It was a game to forget for the Blues, who suffered another injury blow at the back when Nathan Thompson was stretchered off.
And it never really looked like they would salvage anything once Doyle doubled the Latics’ lead just after the interval.
Brett Pitman did pull one back late on to restore some hope, but the hosts were unable to find a dramatic leveller.
Kenny Jackett made one enforced change from the side that beat Bristol Rovers earlier in the week.
Christian Burgess missed out with a calf injury, so Drew Talbot came into the starting 11 and Thompson moved to the centre of defence.
Richie Wellens said in the lead-up to the contest that former Fratton loanee Doyle would miss the contest through injury.
But it appeared to be mind games from the interim Oldham manager, as the striker was named in the team.
And it was Doyle who almost broke the deadlock in a frantic opening to the game, with his 25-yard effort cannoning against the post.
Pitman then tried his luck from a similar distance and a fine strike was expertly tipped over by Latics keeper Johny Placide.
Pompey’s skipper soon met a low cross from Dion Donohue, but Kean Bryan was well placed to clear the danger.
Both sides were looking capable of scoring and Matt Clarke blocked Jack Byrne’s effort before Rob Hunt’s shot swerved wide.
At the other end, Matty Kennedy’s centre was just about taken off the foot of Oliver Hawkins, who was waiting to pounce at the far post.
But it was Oldham who forged ahead on 16 minutes, when Thompson blocked Craig Davies’ effort and Doyle gobbled up the loose ball.
It soon got even worse for the hosts, as their defensive injury curse continued following a collision between Talbot and Thompson.
The latter came off worse and had to be stretchered from the pitch, with Gareth Evans coming on and Talbot moving to the middle.
Both setbacks seemed to affect the Blues and they struggled to find any fluency at either end of the pitch for the remainder of the first half.
A snap-shot from Byrne had to be acrobatically tipped over by Luke McGee to stop the Latics from doubling their lead.
Pompey did carve open one more decent opportunity before the break, however, following a quick move up the pitch.
The visitors were initially able to deal with the attack, but Jamal Lowe picked up the loose ball and struck the post.
Oldham Athletic 1
There was a surprise at the start of the second half, as Hawkins moved to the centre of a makeshift defence, with Evans playing off Pitman.
But it was a slip by Clarke that let in Davies, although the striker’s effort did not cause McGee too many problems.
Oldham did not let their hosts off for a second time, though, and after Hawkins had done well to intercept the danger, Doyle dispossessed Talbot and neatly dinked home his second of the game.
He came close to adding a third on 56 minutes, only for McGee to quickly leave his line and smother Dan Gardner’s ball over the top.
Some more slack defending saw Davies left in acres of space at the far post, although the striker could not quite rise high enough to guide Gevrao Nepomuceno’s cross on target.
Talbot was brought off on the hour mark to be replaced by Kyle Bennett and the newcomer had an immediate chance to reduce the deficit, but could not turn Kennedy’s centre on target.
The third and final switch soon followed, with Ben Close making way for Danny Rose in the middle of the park.
But those changes failed to result in a change of fortunes, as Pompey continued to labour against their energetic visitors.
Pitman was clearly struggling with an injury, but with the Blues having already made all their substitutions, he had to continue
And PITMAN seemed to shake it off, continuing his remarkable scoring streak late on by slotting in from Lowe’s cut-back.
The display of eight minutes of additional time made the Fratton faithful believe that a point could be salvaged.
But despite their best efforts, Pompey were unable to find another goal, as Oldham held on for the victory.
Pompey (4-2-3-1): McGee; Talbot (Bennett 60), Thompson (Evans 22), Clarke, Donohue; Close (Rose 68), O’Keefe; Lowe, Pitman (c), Kennedy; Hawkins
Goals: Pitman 90
Subs not used: Bass, Haunstrup, Naismith, Main
Oldham (4-4-2): Placide; Dummigan, Clarke (c), Bryan, Hunt; Byrne (Menig 88), Fane, Gardner (Banks 79), Nepomuceno (Omrani 65); Doyle, Davies
Goals: Doyle 16, 47
Booked: Dummigan, Bryan, Byrne, Banks, Davies, Placide
Subs not used: Ruddy, Gerrard, Edmundson, Obadeyi
Referee: Craig Hicks
Attendance: 17,848 (466 away fans)
Blues boost promotion hopes
Pompey ran riot at Colchester to strengthen their position inside League Two’s top three.
It was a display of attacking supremacy from the Blues, who arguably deserved to win by more than the four-goal margin.
Eoin Doyle got the ball rolling during a first half that saw the visitors grow stronger as it progressed.
And they moved comfortably through the gears after the interval, as Kyle Bennett, Danny Rose and Michael Doyle all got in on the act.
Paul Cook stuck with the same side that comfortably beat Crawley earlier in the week.
But it was the hosts who made the brighter start and Brennan Dickenson did well down to the left, only to let himself down with the ball into the box.
Pompey soon began to settle and threaten going forward themselves, though, with some neat attacking play.
Eoin Doyle could not quite get on the end of an excellent Carl Baker cross, while a snap-shot from Kal Naismith was safely held by Colchester keeper Sam Walker.
Then when a cross was only partially dealt with by the United defence, Enda Stevens followed up with a volley that Walker was able to collect.
But the Blues did break the deadlock on 22 minutes, with Naismith sending the ball back into the box after his corner had been blocked and Eoin DOYLE heading home from close range.
He was not too far away from adding another soon after, but could not quite get on the end of Bennett’s near-post delivery.
And the on-loan Irishman then capitalised on some hesitancy by George Elokobi to deal with Stevens’ floated pass, only to send his shot over the bar.
Meanwhile, there was little to trouble the visitors at the other end of the pitch, as they comfortably held on to their lead at the break.
Colchester United 0
Colchester replaced Sammie Szmodics with Tarique Fosu at the interval in an attempt to improve their fortunes.
But instead Pompey found themselves further ahead just seconds after the restart – much to the delight of their large travelling army.
And it was BENNETT who doubled his tally for the week when, following good work down the right, Naismith selflessly squared for the winger to tuck home.
United came close to reducing their deficit moments later, but a stretching Chris Porter could not quite reach Dickenson’s cross.
But the Blues were still looking to get forward themselves and when Colchester switched off from a throw, Bennett picked the ball up and neatly side-stepped his man before blazing the shot wide.
Stevens then collected Naismith’s shot free-kick and beat a defender, only to see his arrowed drive deflected just past the post.
United were looking all at sea and it came as no surprise when Pompey extended their advantage further just past the hour mark.
Eoin Doyle did well to slide the ball through to ROSE, who saw his first shot blocked by Walker before neatly dinking home at the second attempt.
The keeper was almost caught out by Naismith moments later, but quickly back-pedalled to claw the ball clear.
Colchester had not created much at the other end and when they finally did get forward, it led to Pompey’s fourth goal.
The visitors broke quickly up the pitch from a corner, with Michael DOYLE surging forward to tuck away his first of the season after Naismith’s initial effort had been saved.
That was Naismith’s last bit of action, as he was immediately replaced by Noel Hunt, with Gary Roberts and Conor Chaplin joining him on the pitch soon after.
And there were no nerves in the closing stages as Pompey comfortably saw the game out to complete an enjoyable afternoon in Essex.
Colchester (4-2-3-1): Walker; Wright (Vincent-Young 66), James, Elokobi, Briggs; Garvan (Bonne 68), Lapslie; Murray, Szmodics (Fosu 46), Dickenson; Porter (c)
Subs not used: Barnes, Wynter, Kinsella, Pyke
Pompey (4-2-3-1): Forde; Evans, Burgess, Clarke, Stevens; Rose, M.Doyle (c); Baker, Naismith (Hunt 74), Bennett (Roberts 77); E.Doyle (Chaplin 84)
Goals: E.Doyle 22, Bennett 46, Rose 61, M.Doyle 73
Subs not used: O’Brien, T.Davies, Linganzi, Lowe
Referee: Darren England
Attendance: 6,504 (2,244 Pompey fans)
Evans and Doyle fire Blues to victory.
Goals from Gareth Evans and Eoin Doyle ensured Pompey beat Blackpool to record a second successive victory.
They totally dominated the first half and probably deserved to lead by more than Evans’ clinical finish.
It was a tighter affair after the break, however, and there were a few nervy moments before the hard-working Doyle opened his account deep into stoppage-time to secure another three-point haul.
Paul Cook stuck with the same side that had beaten Accrington at the same venue less than four days earlier.
And he was rewarded with a bright start for the Blues, who looked to attack their mid-table opponents from the off.
They almost broke the deadlock after just five minutes, only for Gary Roberts to turn Eoin Doyle’s cut-back against the crossbar.
And Roberts then combined well with Kyle Bennett, but the former’s pass was cut-out before it could reach Pompey’s lone striker.
Eoin Doyle did connect with a cross – again from Roberts – moments later and sent a header flying just past the post.
The hosts’ attacking quartet were linking up extremely well, while the impressive Amine Linganzi saw a shot saved by Blackpool keeper Sam Slocombe.
There was not too much happening at the other end, although David Forde was at his commanding best to claim a couple of dangerous balls into the box.
The keeper then had to get down low to his right to push a drive from Kyle Vassell behind for a corner.
But it was the Blues who looked the more threatening side throughout the first half and they deservedly took the lead on 27 minutes.
Enda Stevens’ delivery from the left was missed by Linganzi, but fell for EVANS to lash into the roof of the net.
The advantage was almost doubled a few moments later, with Roberts not quite able to guide a cross on target with his head.
And Eoin Doyle was then inches away from connecting with a superb low cross from Evans that dissected the visitors’ defence.
It was the Irishman who might have added another goal just before the break, but he fired over after Roberts had brilliantly cushioned a long ball forward.
Pompey continued to push forward following the interval and Slocombe was just able to beat Eoin Doyle to Matt Clarke’s long pass.
The visitors did start to have more of an impact as the second half progressed and one corner led to a scramble in the Blues box before Evans eventually hacked clear.
Chances were certainly harder to find since the restart, though, and one acrobatic effort from Christian Burgess flew high over the bar.
Cook made his first change on 68 minutes and it was like for like, as Jamal Lowe made way for Carl Baker.
Blackpool then carved out an excellent opening when Jordan Flores’ low cross found Brad Potts at the far post.
It looked like the midfielder would draw the visitors level, but Stevens launched himself at the ball to make a brilliant block.
Evans had received treatment for a shoulder injury earlier in the half and had to be withdrawn on 75 minutes, with Kal Naismith taking his place at right-back.
Pompey then had a chance to strengthen their lead following a quick break, but Baker was dispossessed before he could shoot.
Jack Whatmough came on for Bennett in the Blues’ final change late on, although for the second game in a row the fourth official initially displayed the wrong number.
And Blackpool then went close to levelling from a corner, but Tom Aldred’s bullet header flew narrowly wide.
The atmosphere understandably grew tenser as the seconds ticked down and Blackpool delivered more crosses into the box.
But with the Seasiders committing men forward, the hosts took advantage to make sure of all three points.
Eoin DOYLE did well to hold off a couple of challenges and find Baker, before collecting the return pass and slotting home his first goal for the club.
Pompey (4-2-3-1): Forde; Evans (Naismith 75), Burgess, Clarke, Stevens; Linganzi, M.Doyle (c); Lowe (Baker 68), Roberts, Bennett (Whatmough 83); E.Doyle
Goals: Evans 27, E.Doyle 90+5
Booked: Burgess, Roberts, Bennett
Subs not used: O’Brien, Rose, Chaplin, Hunt
Blackpool (3-5-2): Slocombe; Aimson, Aldred (c), Robertson; Mellor, Potts (Osayi-Samuel 81), Payne (Matt 81), Flores, Daniel; Delfouneso, Vassell (Odelusi 81)
Subs not used: Lyness, Nolan, Gnanduillet, Cullen
Referee: Darren Deadman
Attendance: 15,132 (216 away fans)
Loan : Preston NE – Portsmouth