After the war of words between them this week, Dunfermline manager Davie Hay got the better of his predecessor Jimmy Calderwood in a close but mediocre contest. A draw looked likely with seven minutes left, but then substitute Simon Donnelly was sent clear by Lee Makel and scored at the second attempt.
Donnelly's scrappy winner gave Dunfermline only their second league win in 10, while Aberdeen have now gone eight games without tasting SPL success and were a pale shadow of the forceful team which beat the Fifers in August and November.
The bad blood of the preceding few days resulted in an explosive start with home skipper Scott Thomson having a header cleared off the line after only three minutes.
Dunfermline dominated the early exchanges and the visitors were forced to bring on Phil McGuire for the injured Michael Hart, but the switch appeared to benefit Aberdeen.
First Ian Campbell had to make a desperate penalty box block after John Stewart had set up top scorer Darren Mackie,
and then former Dons keeper Derek Stillie made a one-handed stop from Kevin McNaughton's low shot.
A mix-up between goal-keeper Ryan Esson and the Aberdeen defence almost gifted the opening goal to Gary Mason, but the momentum had clearly changed and Stillie again rescued his team with an acrobatic stop from Jamie Winters' dipping long-range strike.
Dunfermline re-established control in the lead up to half-time, and striker Jesper Christiansen twice threatened to break the deadlock with a sizzling right-footer which clipped the top of the bar and an angled effort which Esson pushed away.
Billy Mehmet pulled an excellent chance wide at the start of the second period, but he made no mistake six minutes later when he latched on to Andy Tod's knock-down from Thomson's free-kick and smacked the ball low into the far corner form 15 yards.
Noel Hunt was then guility of one of the misses of the season when he hit the post with the goal at his mercy after Mason's left-foot shot had been parried by Esson.
It looked an expensive miss when Aberdeen equalised through defender Zander Diamond following a goalmouth scramble.