Summer signing Ollie Palmer scored to give Mansfield their first goal and win since returning to the Football League.
The visitors started the better of the two teams and James Jennings went close early on with a well-struck volley.
Mansfield keeper Alan Marriot was forced into action and saved well from a Josh Scowen attempt and Paris Cowan-Hall's long-range effort.
But Palmer won it when he pounced on a rebound after Martin Riley's header hit the post and poked in from close range.
VIEW FROM THE DRESSING ROOM
Wycombe manager Gareth Ainsworth told BBC Three Counties Radio:
"It was unrecognisable from the team we had against Morecambe or Leicester and there's no rhyme or reason to it.
"We were poor today, we were very poor and I won't let that happen again.
"There's not many positives I can take from that match.
"I need to get the belief back in them and get them playing football."
Wycombe Wanderers 01 Ingram 02 McCoy 03 Dunne Booked 05 Stewart 30 Doherty 04 Scowen Booked 09 Spring 12 Cowan-Hall (Wood - 66' ) 23 Arnold Booked (Kretzschmar - 76' ) 18 Kuffour 29 McClure (Morgan - 57' ) Substitutes 41 Harrison 06 Johnson 11 Wood 22 Kretzschmar 07 Morgan 16 Pittman 20 Craig Mansfield 01 Marriott 02 Sutton 04 Dempster Booked 06 Riley 17 Beevers 11 Clucas (Palmer - 69' ) 16 Jennings 19 Clements 23 McGuire 18 Hutchinson Booked (Howell - 90' ) 24 Andrew (Rhead - 74' ) Substitutes 33 Mitchell 12 Tafazolli 09 Rhead 10 Stevenson 13 Howell 20 Meikle 36 Palmer