A single header from Conor Chaplin was enough for Pompey to record their third 1-0 win away from home this season despite being down to ten men in the second half.
In what was, in truth, a poor game of football, Chaplin's quality was ultimately the difference as Paul Cook's men dug in once Amine Linganzi was sent off for a two-footed lunge - a decision he can have no complaints about, even if the decision in real time seemed harsh from a Pompey perspective.
Prior to that, the first half of this match saw little in chances created wih both sides lacking in quality when going forward. Then, out of nothing, Christian Burgess' pinpoint long diagonal into the box was met by the head of Chaplin who rose in between two defenders to score.
Will Norris had to gather Kyle Bennett's stinging shot from the edge of the box at the second attempt in what was otherwise a dull 45 minutes.
The second half began with Chaplin looking to double his tally, only to fire over after beating a couple of Cambridge defenders. The highlight of the second half from the travelling fans' point of view was the minutes' applause from fans all around the ground on the 53rd minute for Pompey fan Gary Martin who tragically died during the week - yesterday would have been his 53rd birthday.
Cambridge's best chance of the game came soon a loose ball looped into the path of Ben Williamson just two yards out from goal but he fired wide when it looked easier to score.
Linganzi's dismissal came after that and from then on the last half hour saw the Pompey defence repel Cambridge's attacks expertly was Burgess and Clarke dealt with any dangerous crosses coming into the box and if they were unable to get to the ball then the commanding David Forde was there to take the ball and calm proceedings down.
That was just as well because clearances were often collected by the home side despite the best attempts of Gary Roberts and Noel Hunt to pressure them into giving possession away. Thankfully, some outstanding defending and Cambridge's own ineptness at creating chances meant that the ten men of Portsmouth were able to hold on and claim a valuable three points in their bid for promotion.
For those who have watched Pompey regularly this season, it is difficult to fathom where this kind of gritty performance came from as it seemed inevitable that as soon as Cambridge had the numerical advantage that they would eventually find some way of scoring.
However, Burgess was a colossus at the heart of the Portsmouth defence and Clarke next to him also played his part in keeping the Cambridge attack at bay - further cementing the pair as Paul Cook's first-choice central defensive partnership.
It was mentioned in the previous preview article that Michael Doyle would have to be back to his best to win the midfield battle and suffice to say, he was up for the challenge as he produced his best performance of the season.
The manager, who was criticised last week for his apparent lack of tactical awareness, deserves some credit for this result too as he reacted to Linganzi's dismissal with clever substitutions that saw Bennett sacrificed for Danny Rose and Hunt brought on for Chaplin as he imposes a more physical presence whilst retaining the will to chase down the opposition.
People have been saying that this victory, in particular the manner of it, may be a turning point in this season as Pompey have proved that they can win ugly.
They may be right, but in perspective, all three of Pompey's wins on the road this season have been 1-0 and the opposition have been particularly poor at home, especially when it comes to scoring goals.
Whilst the nature of yesterday's victory was sweet (even if the game wasn't good to watch), it's going to take more than a few narrow wins against poor teams on the road to convince people that this squad is capable of winning automatic promotion.
As it stands, the result keeps Portsmouth in the play-off places and now only three from Doncaster in third position. It will still be a while yet before the league table truly takes shape (as is always the case for League Two) but next week the focus turns to the FA Cup and Wycombe Wanderers.
Pompey Player Ratings
David Forde: 7 - Didn't have a save to make but such a commanding and assuring presence.
Gareth Evans: 6 - Steady enough.
Christian Burgess: 9 - Won virtually everything in what was one of the best performances of his Pompey career.
Matt Clarke: 8 - Rock solid.
Enda Stevens: 6 - Did his part.
Michael Doyle: 8 - Produced the kind of performance that saw him crowned Pompey's player of last season.
Amine Linganzi: 6 - Did a good job before silly challenge.
Gary Roberts: 6 - Worked hard even if the quality wasn't there.
Carl Baker: 5 - Struggled to have much of an impact.
Kyle Bennett: 6 - Posed some problems in the first half.
Conor Chaplin: 7 - Instinctive header underlines his quality.
Substitutes
Liam O'Brien
Tom Davies (Roberts 93): N/A - Brought on to see out the last two minutes.
Adam Buxton
Danny Rose (Bennett 62): 6 - Slotted in fine.
Milan Lalkovic
Noel Hunt (Chaplin 63): 6 - Chased everything.
Michael Smith