Anthony Stewart scored a dramatic last-minute winner to earn Wycombe back-to-back victories and extend Fleetwood's winless streak to four matches.
The Cod Army bossed the opening stages, but the hosts came close when Sam Wood scuffed Josh Scowen's corner wide.
The visitors began to create chances as top scorer Junior Brown was denied by a flying save from Jordan Archer.
But in the dying stages, Stewart had an effort cleared off the line, before turning in the resulting corner.
The winner was 20-year-old Stewart's first goal for his boyhood club and dents Fleetwood's play-off hopes, leaving them six points adrift of the top seven in League Two.
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Wycombe manager Gareth Ainsworth told BBC Three Counties Radio:
"I thought we were absolutely fantastic in the first half.
"It's a good scalp for us and my lads are really happy and I'm very proud of them.
"Second half I thought there was only one team in it.
"They had a couple of headers from distance but we limited them to that.
"The fans were fantastic. Hopefully we can kick on higher and see where we get to."
Fleetwood manager Graham Alexander told BBC Radio Lancashire:
"I wouldn't have been happy with 0-0. I thought we created enough chances to win the game, and then to lose in the last minute is massively disappointing.
"I don't think we deserved to lose it but I thought we need things to encourage Wycombe and that's what our downfall was."