Robert Koren scored to give Nick Barmby the perfect start to his reign as Hull's full-time manager as his side beat Peterborough to go fifth.
Posh started strongly, with Emile Sinclair and Lee Tomlin going close.
Koren had chances before he picked up Aaron McLean's cross and fired in low past Joe Lewis.
The visitors were unlucky not to be awarded a penalty when goalkeeper Vito Mannone appeared to bring down Daniel Kearns, but the Tigers held on.
Substitute Joe Dudgeon could then have made it safe but was off target on the hour.
Lewis also made fine saves to deny Robbie Brady and McLean, before Peterborough's Paul Taylor spurned a late chance to snatch a point in added time.
Defeat means Darren Ferguson's side have not won in four games.
Hull City manager Nicky Barmby:
"We rode our luck in the first half hour and maybe they should have had a penalty.
"If it had happened to us we would have been disappointed not to get a penalty. But we have had a few penalty shouts go against us recently, so maybe it evened itself out.
"Then in the second half I thought the shape of the team was a lot better. All credit to the lads as they worked it out what they should be doing and we showed what we can do. We could have scored a lot more goals than we did."
Peterborough United manager Darren Ferguson:
"The penalty incident is such a bad decision. When we asked the referee at half-time why he didn't give it, he said that the goalkeeper made an attempt to win the ball but didn't win it. So he was basically saying it was a penalty.
"The boy (Kearns) has got a six-inch gash in his leg. But what can you do? However, we were excellent and that is the best we have played for a while. We should have got a result.
"Emile (Sinclair) had two great chances early on and did everything right. He was just unlucky. We were far more fluid in the first half, but we didn't test their goalkeeper enough in the second half.
"I'm happy with the performance as a whole though and there are a lot of positives to take from the game."