Despite Nikki Bull’s first-half penalty save, Wycombe looked to be heading for a first defeat in five games thanks to Daniel Powell’s goal for the Dons a minute after the restart.
But Beavon popped up to head home a Gareth Ainsworth corner in injury time to notch his 22nd of the season, keeping the Chairboys outside the relegation zone by a point.
In an open first-half the only thing standing in the way of a goal was Wycombe’s Bull, the goalkeeper denying Jay O’Shea from the spot and again from the rebound after Marvin McCoy brought down Alan Smith in the box after just 10 minutes.
But his hard work was undone less than a minute after the restart as Charlie MacDonald flicked a long ball into the path of Powell who slotted the ball home with ease.
Ben Strevens headed over from point-blank range after 50 minutes but his blushes were spared by strike partner Beavon to stretch Wycombe’s unbeaten run to five games.