Pompey thrashed Cheltenham 6-1 to secure the League Two title on a memorable afternoon on the south coast.
They became only the fifth team to win all four divisions after both Plymouth and Doncaster failed to secure three points.
Daniel O’Shaughnessy’s own-goal opened the scoring at Fratton Park, but the lead was a slender one at the break.
It all changed in the second half, however, as Kyle Bennett, Jamal Lowe and Gareth Evans found the target – the latter from the penalty spot – while Kal Naismith bagged a brace.
Fans then flooded onto the pitch at full-time to begin a party that will likely last for quite a while.
Paul Cook stuck with the same side that won at Mansfield the previous week, meaning that it was Conor Chaplin who again led the line.
But it was a Robins player who inadvertently gave the hosts a welcome lead with just 13 minutes on the clock.
Enda Stevens – who collected The News/Sports Mail Player of the Season award before kick-off – delivered a low cross that O’Shaughnessy deflected into his own net.
Chaplin had a chance to double the advantage soon after, but his fierce drive was kept out by Scott Brown.
Cheltenham were not creating too much at the other end, although David Forde got down to his left to keep out Harry Pell’s effort.
The Blues were looking more threatening, meanwhile, and when a free-kick was played to Carl Baker, his curling shot was deflected inches past the post by the knee of Danny Wright.
The visitors grew stronger as the first half progressed and Forde made a comfortable save to deny Billy Waters.
Then, after the keeper did well to keep out Dan Holman’s strike, Danny Rowe curled the ball narrowly wide.
Bennett had a shot saved by Brown, while a stretching Chaplin could not quite reach Naismith’s centre.
But Cheltenham almost grabbed a leveller just before the interval, Dan Holman finding Rowe and the midfielder firing in a shot that was deflected narrowly over.
Cheltenham Town 0
There was also a great chance for the visitors moments after the restart, but Danny Wright could only head Kyle Storer’s cross wide from close range.
Holman then had a shot that was racing towards the net before Forde dived to his right to push the ball clear.
But the Blues almost had a second when Danny Rose unleashed a fierce volley that cannoned back off the underside of the crossbar.
Cook made a double switch just past the hour mark, with Baker and Chaplin making way for Lowe and Gary Roberts.
And Pompey soon doubled their advantage, as BENNETT fired in a shot that took a wicked deflection to leave Brown stranded.
That was the cue for the floodgates to open and, following a quick counter, Bennett slipped the ball through for NAISMITH to calmly slip home.
It was substitute LOWE who was next to get in on the act on 72 minutes when he found the bottom corner from a tight angle.
And when Roberts was tripped in the box by Liam Davis, referee Christopher Sarginson pointed to the spot, with EVANS stepping up to slam home the resulting penalty.
The fans were celebrating in the stands with news coming through that both Doncaster and Plymouth were being held.
Pompey had certainly done their job, although Cheltenham pulled a goal back through substitute James Dayton.
That failed to stop the hosts’ attacking charge, however, and Bennett’s strike was superbly saved by Brown.
NAISMITH did grab a sixth goal on 85 minutes, with Michael Doyle sending a ball over the top and Pompey’s top scorer calmly slotting into the net.
All the attention now was to what was happening at Grimsby and Hartlepool, with plenty of fingernails being chewed.
Fans ran onto the pitch in celebration at the final whistle, with news filtering through that Plymouth could only draw.
And when Doncaster’s match at Hartlepool finished in defeat, it was confirmed that Pompey were League Two champions.
We’re on our way.
Pompey (4-2-3-1): Forde; Evans, Burgess, Clarke, Stevens; Rose (Aborah 71), M.Doyle; Baker (Lowe 61), Naismith, Bennett; Chaplin (Roberts 61)
Goals: O’Shaughnessy 13 (og), Bennett 62, Naismith 66, 85, Lowe 72, Evans 75 (pen)
Subs not used: O’Brien, Whatmough, Linganzi , Lowe, Roberts, Kabamba
Cheltenham (4-4-2): Brown; Cranston (Barthram 66), O’Shaughnessy, Boyle, Davies; Pell (Dayton 54), Storer (c), Rowe, Waters; Wright, Holman (Munns 71)
Goals: Dayton 78
Subs not used: Kitscha, Winchester, Downes, Wootton
Referee: Christopher Sarginson
Attendance: 17,956 (545 away fans)