Dons striker Aaron Wilbraham’s double had cancelled out Alex Revell’s brace but Betsy fired home five minutes into injury time to hand the Chairboys their third straight win.
Revell put Wycombe ahead against the run of play in the 29th minute, stroking a precise first-time finish past goalkeeper Willy Gueret from Betsy’s cutback. Chairboys defender Lewis Hunt had a header cleared off the line by Luke Howell before Wilbraham equalised for the Dons on the stroke of half-time, nodding in Mark Randall’s free-kick from close range.
Wycombe upped the tempo after the break and Jon-Paul Pittman fired wide when clean through before Revell restored their lead in the 64th minute. He raced onto Betsy’s defence-splitting pass and slotted the ball underneath Gueret one-on-one for his fourth goal in two games.
Wilbraham made it 2-2 in the 75th minute when he scuffed in the rebound after Sam Baldock’s penalty had been saved by Tom Heaton, following Gareth Ainsworth’s foul on Luke Chadwick in the box.
But Betsy wriggled free in a crowded box and blasted the ball past Gueret at the death to hand Wanderers their first ever Bucks derby win.