Conor Chaplin headed home his fifth goal of the season to ensure Pompey kept up their impressive record over Cambridge.
He converted Christian Burgess’ cross midway through the first half of a game that otherwise failed to excite.
But the Blues had to play the final 30 minutes with only 10 men following a lunge from Amine Linganzi.
Paul Cook made one change from the side beaten by Notts County at Fratton Park the previous week.
That came in the centre of defence, where Tom Davies dropped to the bench to make way for Matt Clarke.
There were plenty of Pompey connections in the hosts’ set-up, with James Dunne and Adam McGurk both starting for Shaun Derry’s side.
It was not a contest to excite those in attendance at Abbey Stadium – including 1,850 who travelled up from the south coast – in the opening stages.
A couple of Blues breaks petered out before the defence could be properly troubled, while David Forde comfortably dealt with McGurk’s header.
The same player then tried an acrobatic over-head effort from 25 yards that sailed over the bar as the first half continued to plod along.
It was the same story at the other end of the pitch, where Gary Roberts laid a free-kick off to Michael Doyle, only for the skipper to take a total air-shot from the edge of the box.
But then, from nothing, Burgess broke clear down the right and Pompey found themselves in the lead on 24 minutes.
The defender launched the ball into the box from just inside the opposition half and CHAPLIN – the smallest player on the pitch – sent a header looping into the net.
Burgess then breathed a sigh of relief seconds later when Uche Ikpeazu went down under his challenge.
Referee Ross Joyce was unimpressed by the home side’s appeals, however, with Dunne’s protests earning him a yellow card.
Pompey were now enjoying a spell of pressure and Will Norris did well to parry away Kyle Bennett’s fierce effort, while a low Enda Stevens cross had to be hacked behind.
This was a few minutes of excitement in an otherwise dull half of football, however, as the interval arrived without any more noteworthy moments.
Cambridge United 0
There was a chance for the Blues at the start of the second half when Doyle played a clever pass over the top.
Chaplin latched onto it and did well to beat his man and burst into the box, but then bent a shot wide of the post.
Both sets of supporters applauded in the 53rd minute in memory of Pompey fan Gary Martin, who would have turned 53 today.
On the pitch, the visitors were almost caught out when they failed to clear the danger and the ball fell for Ben Williamson.
The striker was left with only Forde to beat, only to drag his shot wide and let Pompey off the hook.
But the Blues were dealt a huge blow when they were reduced to 10 men just past the hour mark.
Linganzi lunged into a challenge on Conor Newton in the centre circle and although there did not appear to be too much contact, his studs were showing and Joyce brandished a red card.
Cook immediately looked to shore up his side with a double substitution, as Bennett and Chaplin made way for Danny Rose and Noel Hunt.
Cambridge set about trying to make their numerical advantage count and when Piero Mingoia’s cross was headed clear by Burgess, Dunne saw his follow-up deflected narrowly wide.
But with Burgess and Clarke expertly marshalling things at the back, Forde was enjoying a largely untroubled afternoon.
And the Blues saw out the final few moments to secure a return to winning ways on one of their favourite hunting grounds.
Cambridge (4-4-2): Norris; Halliday (Pigott 83), Legge (c), Roberts, Taylor; Mingoia, Dunne, Clark (Newton 58), Dunk; McGurk (Williamson 33), Ikpeazu
Booked: Dunne, Halliday, Ikpeazu
Subs not used: Gregory, Long, Coulsen, Gosling
Pompey (4-2-3-1): Forde; Evans, Burgess, Clarke, Stevens; Linganzi, Doyle (c); Baker, Roberts (T.Davies 90+3), Bennett (Rose 62); Chaplin (Hunt 63)
Goals: Chaplin 24
Sent off: Linganzi
Booked: Chaplin, Doyle, Hunt, Roberts
Subs not used: O’Brien, Buxton, Lalkovic, Smith
Referee: Ross Joyce
Attendance: 6,397 (1,850 Pompey fans)