And the Dons have now taken 16 points out of a possible 18 and sit three points clear in second place in the SPL.
The game opened brightly with a spectacular effort straight from kick-off by Scott Severin that forced Dorus De Vries to back-pedal furiously and grab the ball under the crossbar.
But the Pars looked menacing going forward and it took a wonderful save from James Langfield to tip over a blistering long-range effort from Scott Muirhead.
But the best chance of the half fell to Chris Clark when Gary Dempsey's cross found him unmarked six yards out. He made a good connection with his header, but it was the perfect height for De Vries to dive to his right and push the ball clear.
Defences were on top in the first half but a shocking error from Greg Shields gifted the home side the lead.
Barry Nicholson's long ball got caught in the defender's feet and Lee Miller robbed him and coolly slotted home from 15 yards.
Another blunder, this time from Scott Wilson, allowed Aberdeen to stretch their lead. The big defender let Russell Anderson's long ball bounce over him and Darren Mackie nipped in to lob the ball over the stranded De Vries.
And a breakaway goal five minutes from time rounded off the scoring. Darren Young was caught in possession at the edge of the Aberdeen box and Mackie ran fully 60 yards before guiding a low right-foot shot past De Vries.
The result leaves Dunfermline anchored at the bottom and they will have to eliminate defensive errors if they are to have any chance of avoiding relegation.