Brett Pitman was the match-winner, finishing from the penalty spot in the 72nd minute to clinch a 2-1 victory over AFC Wimbledon.
Earlier, Lyle Taylor’s 50th-minute penalty had cancelled out Ben Close’s maiden Fratton Park goal.
But the Blues secured the result they craved as they bounced back from a disappointing defeat at Shrewsbury to regain seventh spot in League One.
Pompey’s boss said: ‘As the game wore on I felt we opened up more, played more constructive football and basically had more chances and more shots.
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‘It was hard-fought, we got in front twice and saw it out the second time. I thought both were penalties, they were the key moments and the key decisions.
‘The way we finished the game might have coincided with them going away from a back five, which had made it difficult for us to break them down.
‘They had to attack us and go to a back four, so [Gareth] Evans was finding space on the right and driving forward.
‘It’s a good way to bounce back from a defeat and, looking at the Christmas period as a whole, we can look forward now to Northampton, very quickly followed by Bristol Rovers on Monday.’