TWO first half goals from John O'Flynn ended the Dons' unbeaten start to the campaign.
The Irishman's low, deflected shot from the edge of the box put the Grecians in front and he should have doubled his tally after rounding the keeper.
But the striker made amends, finishing a fine counter attack from close range after Dave Wheeler's cross had created the opening
Chances were limited after the break as Wimbledon's best chance saw Andy Frampton's header cleared off the line and boss Neal Ardley conceded his players had been beaten by the better team.
Line up: Warner, Fuller, Bennett (Weston 39), Frampton, Kennedy, Sweeney, Luke Moore, Pell, Porter (Francomb h/t), Smith, Midson. Subs not used: Brown, Fenlon, Sammy Moore, Arthur, Sheringham.