Pompey fought from behind to beat Cambridge and give their League One promotion hopes another boost.
A Danny Andrew header was adjudged to have crossed the line, but Kusini Yengi levelled from the penalty spot before the break.
Myles Peart-Harris then completed a neat passing move to give the Blues the lead, while a fine Abu Kamara strike made sure the points would be remaining on the south coast.
John Mousinho made two changes from the side that won on the road at struggling Carlisle at the weekend.
Yengi and Kamara were both added to the forward line, as Colby Bishop and Callum Lang dropped to the bench.
Pompey looked to make a fast start, with Yengi and Peart-Harris swapping passes as they advanced down the pitch before Andrew was able to hack the ball behind.
Sean Raggett then got on the end of a Paddy Lane corner, but his header was diverted from its intended target by Lyle Taylor.
Cambridge looked to capitalise on a rare defensive mix-up at the other end, with Joe Rafferty managing to get in the way of Jack Lankester’s effort.
The hosts were soon back on the attack, with Conor Shaughnessy beating two men and threading a pass through for Lane, whose low ball across the face of goal was scrambled clear.
But it soon began to turn a bit flat, with the Blues struggling to turn their possession into genuine openings in the final third.
And they were dealt a blow when Tom Lowery pulled up injured off the ball, with January arrival Owen Moxon on to replace him.
There was more bad news on 38 minutes, when Andrew got on the end of Sullay Kaikai’s corner and headed towards goal.
Will Norris clawed the ball away, but an assistant’s flag was raised to suggest it had crossed the line, not that Pompey’s furious keeper was convinced.
There was an almost an immediate response, with Yengi fizzing a fierce low drive narrowly past the post.
An equaliser did arrive before the break, however, after Ryan Bennett lunged in on Yengi inside the box.
Referee Sam Allison pointed straight to the spot and the defender was perhaps lucky to escape further punishment, having been booked earlier in the contest.
Cambridge keeper Jack Stevens did his best to delay the penalty, but YENGI kept his composure and slammed the ball straight down the middle.
Half Time: Pompey 1 Cambridge 1
The hosts were hoping for a bit more forward fluidity following the restart, but were still finding their opponents a tough nut to crack.
United were defending resolutely, with four men immediately around Peart-Harris when he burst into the area.
They kept plugging away, though, and the ground came alive when a passing move finally came off just before the hour mark.
Moxon found Peart-Harris and his pass was neatly controlled by Yengi, who laid the ball off for Lane inside the box.
The Northern Ireland international sent a low delivery across the face of goal and PEART-HARRIS slid in to open his Blues account.
Cambridge tried to hit back at the other end, although Kaikai could only find the side netting after tricking his way past Rafferty.
And Pompey soon had a cushion thanks to a moment of magic from KAMARA, who collected Lane’s pass, cut onto his left and hit a dipping shot that crashed into the net off the underside of the bar.
That was the cue for a couple of changes, as Yengi and Peart-Harris made way to standing ovations, replaced by Bishop and Lang.
The hosts were still looking to cause problems, although the urgency had understandably dissipated somewhat.
Mousinho brought on a couple more players for the closing stages, with Josh Martin and Jack Sparkes introduced for Kamara and Lane.
And the closing stages passed by without much incident, as the Fratton faithful celebrated another valuable victory.
Pompey (4-2-3-1): Norris; Rafferty, Raggett, Shaughnessy, Ogilvie; Lowery (Moxon 36), Pack (c); Kamara (Martin 85), Peart-Harris (Lang 72), Lane (Sparkes 85), Yengi (Bishop 72)
Goals: Yengi 44 (pen), Peart-Harris 59, Kamara 71
Booked: Norris, Sparkes
Subs not used: Macey, Towler
Cambridge (4-1-4-1): Stevens; Gibbons (L.Bennett 72), R.Bennett, Morrison, Andrew; Cousins (May 76); Kaikai (Bonne 76), Lankester, Thomas (Kachunga 72), Brophy (Digby 76); Taylor
Goals: Andrew 38
Booked: R.Bennett, Lankester, Stevens, Gibbons, Morrison
Subs not used: Mannion, Rossi
Referee: Sam Allison
Attendance: 19,445 (305 away fans)