Ross Forbes and Danny Grainger, both signed during the transfer window, contributed debut goals.
Dunfermline should have gone ahead midway through the first half when Ryan Wallace was clean through but shot wide.
Forbes broke the deadlock a minute from the break when he took advantage of a mistake by Joe Mbu. Wallace made it 2-0 in the second half before Grainger adding the third. Paul Willis scored a late consolation for the home side.
Ayr United held off Arbroath's second-half fightback to win 3-2 at Gayfield. With the wind behind them, Ayr were 3-0 up within half an hour as Michael Moffat scored twice to take his season's tally to 20. Michael Donald also netted. Bobby Linn and Leighton McIntosh reduced the deficit after the break.
Forfar Athletic and Airdrieonians shared a 1-1 draw at Station Park. Forfar led through Omar Kader with Jim Lister equalising. At Ochilview, Stenhousemuir and Stranraer also drew 1-1. Andy Stirling's 88th-minute looked to have won it for the visitors, but Eddie Malone equalised deep in injury-time.