Nathan Redmond's stunning late finish sealed victory for Birmingham as they broke Portsmouth's resistance and moved up to third in the Championship.
Portsmouth had the best chance of an even first half as Joel Ward was denied at close range by Birmingham goalkeeper Boaz Myhill.
Birmingham applied pressure in the second period with Jordon Mutch's 25-yard strike hitting a post.
Redmond's swivelled volley then sealed victory in the 86th minute.
DID YOU KNOW?
- This was Birmingham's 41st match of a busy campaign, in which they have played 11 more fixtures than Portsmouth.
The highly-rated 17-year-old substitute was brought on to bring much-needed life to City's attacking play on the hour-mark.
And his winner hauled Birmingham to within two points of second-placed Southampton, with leaders West Ham six points ahead.
It was Hughton's side who started with the greater purpose, Marlon King's pull-back just failing to find a blue shirt before Keith Fahey tested Stephen Henderson from distance.
Marko Futacs wasted a great chance to test Myhill when he blazed over from 12 yards out from Kelvin Etuhu's low cross. And Myhill was again impressive in the 40th minute, keeping out Ward's 10-yard shot.
City started the second with renewed vigour, but they were still struggling to find a way through.
Two good chances came on the 70-minute mark as Adam Rooney's close-range effort was smothered by Henderson, then Curtis Davies flicked the ball narrowly wide from six yards.
Mutch then struck the woodwork with a low strike from distance, before Birmingham turned the screw and Redmond clinched victory.
Birmingham manager Chris Hughton:
"Nathan Redmond is a wonderful player.
"He's a real talent, we genuinely don't like to get too carried away about players because we've seen it before when you get a player who doesn't get to the levels you think he is going to.
"At the moment I think we've managed him quite well."
Portsmouth boss Michael Appleton:
"I'm hoping for news [about investment] over the next couple of days because the longer it goes on, obviously, the more difficult it's going to be to keep morale up and keep the players in a positive frame of mind.
"They're a decent bunch of lads, who've had to take a lot of hits over the last couple of months or so with everything that's going on, especially in the last week not being paid.
"I can't really any ask for any more effort.
"I tried to remind them before the game this evening of why we all started playing football in the first place, it's because we love the game and we enjoy it."
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