Millwall's unbeaten run at The Den came to a shuddering halt as a spirited Wycombe side snatched all three points in a frustrating encounter for the home side.
Despite enjoying the lion's share of possession, The Lions could not find a way past visiting keeper Scott Shearer and his stubborn back line. Chris Hackett and Danny Schofield had Millwall's best chances. Hackett drew a fine save out of Shearer with a dipping free-kick, whilst Schofield's rasping shot needed a strong hand from The Chairboy's custodian to send it wide.
But Wycombe were by no means second best, and Chris Westwood rose highest to bury a header past David Forde before Kevin Betsy made the points safe, escaping the attentions of Jack Smith and coolly finishing.
Millwall made only two changes to the side that drew on the road against Brentford a week ago. Alan Dunne dropped to the bench to make way for a return to the first team for Darren Ward. The other change saw top scorer Neil Harris miss out with a back problem, his place in attack taken by Steve Morison.
It was Millwall who fashioned the first chance of the match. Paul Robinson's long free-kick was knocked down for Marc Laird, who had time to swivel and snap off a shot from the edge of the box. Shearer, however, was well placed to gather.
The wet conditions made it hard for both teams to find their rhythm, but Wycombe's recent loan signing Gareth Ainsworth was understandably eager to impress. In the 12th minute, his over-zealousness led him to accidentally raise a boot to the face of Tony Carig. Unfortunately for The Lions' left back, his afternoon was over, and Andy Frampton entered the fray.
Wycombe very nearly snatched the lead four minutes later. A Scott Davies' free-kick found Westwood at the back post but the defenders downward header bounced over the bar.
Back came Millwall, and Hackett's teasing free-kick drew a diving save out of Shearer. From the resultant corner, Hackett found Frampton charging in, but the substitute's header flew inches wide.
Ainsworth, by this time roundly booed by the home fans, showed his determination once again with a driving run at The Lions defence. Creating space, he managed to get a shot off, but Forde saved with ease.
Not to be out done, Millwall put together a beautiful move, with one touch passing setting Morison free behind The Chairboy's defence. The former Stevenage striker was in the clear, but checked his run just a little too late and was only stopped by the linesman's flag.
In the ascendancy, The Lions could, and perhaps should, have taken the lead. A carefully weighted through ball from Laird found Price in acres of space, but the tall Welshman lost control of the ball in his feel and Wycombe could clear. The visitors' problems worsened on 24 minutes, after a heavy tackle on Jon-Paul Pittman left him in a heap. Unfortunately he was stretchered off, with Stuart Beavon coming on.
The play settled into a stagnant stalemate, with home crowd growing increasingly frustrated. However, with seconds to go, there was just time for Smith, Laird and Schofield to combine down the right, and the full-back floating over a good-looking cross that Shearer needed to palm over with Morison lurking.
The second half opened in a more positive fashion. Hackett broke away after a fine Ainsworth cross evaded everyone in the Millwall box and found Laird. The Scot did well to pick out the run of Schofield on the left and when he drove at Lewis Hunt, he found an angle to test Shearer with a drive that the Wycombe keeper did well to beat wide.
Schofield was involved again seconds later, when his back-post cross so nearly found Morison.
The Chairboys were not out of it entirely and fashioned a chance of their own minutes later. Ainsworth wriggled free down the right, whipped in a cross that was cleared straight to Tommy Doherty. The former QPR man shaped to shoot with his right, cut inside and bent a left-foot strike straight into the grateful arms of Forde.
It proved a warning, as with their next attack, Wycombe took the lead. Davies' pinpoint corner met the head of Westwood who guided the ball beyond Forde.
In need of reiforcements, Jackett introduced Dave Martin for the hardworking Laird after on the hour.
Try as they might, Martin and Millwall could not find a way through a resolute Chairboys rearguard, trying desperately to hold on to what would be their first victory under Gary Waddock.
Kenny made his next change on 70 minutes, with Morison making way for Ashley Grimes.
It made little difference as Wycombe extended their lead on 72 minutes, as neat build up play released Kevin Betsy who raced away from a retreating Smith to calmly slot home past the advancing Forde.
Millwall went in search of anything that might bring them back in the game, but Wanderers had taken heart from going ahead and showed greater confidence. Defending well, they looked dangerous on the counter, with the pace of Beavon, Davies and Betsy meaning The Lions' backline were not given a second's rest.
Millwall continued to be frustrated, but Wycombe emerged victorious, their first win under their new manager.

Millwall: Forde, Smith, Robinson, Ward, Craig (Frampton, 12mins), Hackett, Abdou, Laird (Martin, 60mins), Schofield, Morison (Grimes, 70mins), Price.
Subs not used: Sullivan, Dunne, Bolder, Grabban.

Wycombe: Shearer, Hunt, Oliver, Westwood, Woodman, Ainsworth, Doherty, Mousinho, Davies, Betsy, Pittman (Beavon, 24mins).
Subs not used: Young, Bloomfield, Spence, Duberry, Green, Westlake.

Goals: Westwood (52), Betsy (72)

Bookings: Davies (Wycombe) (37)

Referee: RJ Booth

Attendance: 9,728 (Away 388)