Ryan Taylor was the match-winner as Pompey hung on for a vital 1-0 win over AFC Wimbledon.
The striker netted the only goal of the game with a fine header from Daniel Alfei’s searching cross that found the bottom corner early in the second half.
After a dreadful first-half display, the Blues were better after the break as they began to play with some much-needed tempo and more commitment.
But having got a goal ahead, the Dons looked the more likely to find an equaliser as keeper Trevor Carson made brilliant save to deny Alan Bennett’s close-range header.
And with the tension cranked up as the final whistle approached, Pompey resorted to desperate defending but crucially held out to claim a much-needed three points.