Victory over title-chasing Wigan has taken Pompey to the brink of the play-off places.
Only goal difference is now keeping them behind Peterborough and Charlton, who sit in fifth and sixth spot respectively.
Brett Pitman opened the scoring at a sodden Fratton Park, hitting his 20th goal of the campaign from the penalty spot following a foul on Ben Close.
Jamal Lowe then added a vital second half strike before Will Grigg reduced the deficit late on to create a nervy finale.
But the hosts held on to secure all three points and Kenny Jackett was delighted with the performance from his in-form troops.
The Blues boss said: “It was a big win for us as we continue to chase the top six – and it’s the fourth on the trot for us. We’re on a great run at the right time.
“Wigan are a very good team and our keeper had to make two outstanding saves during the second half.
"We’re on a great run at the right time."
“To score two against a side like them is a really positive thing because they’ve kept 23 clean sheets out of 38 matches, which is exactly why they are where they are.
“We were impressive for the first hour and did well to break up Wigan’s play, limiting them to half-chances and creating opportunities on the turnover.
“I’m delighted for Brett because he was the right person at the right time to put that penalty away and to score 20 goals in a season is a big achievement.
“That gave is something to work towards and Jamal then chipped in with a good turn and finish, which turned out to be the winner.
“Wigan’s pressure came from about 60 minutes onwards and we had make sure that we stuck to the game-plan, without stepping back too deep.
“We needed to believe in ourselves more towards the end and try to get up the pitch and we need to keep pressing if we want to be a really good side.
“I felt that Nick Powell got in and was allowed too many headers, so that’s where we have to improve if we want to be where Wigan are.”
Pompey will now look to keep their run going with three successive away fixtures at Rochdale, Plymouth and Bradford.
Jackett said: “There will now be a terrific focus on the games going forward. It’s good to be in this situation and chasing one of those three promotion places.
“It’s open of a number of teams now and I’m delighted to say that we are very much still one of them.”