Andy Barrowman scored a double and set up the other two, netting his first midway through the first half and then laying on the second for Jordan McMillan before half-time.
Ryan Thomson scored Dunfermline's third after more good work from Barrowman, who then lobbed Andy McNeil for the fourth.
At the other end of the table, Dumbarton collected their first point of the season in a 3-3 draw at home to Hamilton Academical.
But it was scant consolation as they had led 3-1 going into the final few minutes, only for James Keatings to reduce the deficit and then level deep into injury-time to give a young Hamilton side a point that had looked beyond them.
Ali Crawford, who also hit woodwork late in the game, gave Accies the lead but Lee Kilday turned a Jim Lister flick into his own net for the equaliser before half-time.
Martin McNiff was denied by Kevin Cuthbert and Lister hit the post as Dumbarton opened the second half on top. It was no surprise when Lister headed them in front from a Mark Lamont cross. The points looked secure when Bryan Prunty made it 3-1 but Keatings had other ideas.
A measured strike from Stephen Stirling gave Morton a 1-0 win over Raith Rovers at Cappielow in a match that could have gone either way. For once, Brian Graham's goal touch deserted him and he could not tuck away a goal for Raith in spite of having chances.
David Smith also missed a great opportunity in the first half but Stirling's second-half goal, which came when he curled the ball out of David McGurn's reach from just outside the area, proved sufficient. Both teams had chances after that but Morton kept their noses in front to move up to third in the table.
Falkirk and Airdrie United drew 1-1 at the Falkirk Stadium. The hosts took the lead when Sean Higgins was tripped by David Lilley as he broke into the box and Stewart Murdoch calmly slotted home the resultant penalty.
Two minutes later, Cameron MacDonald denied Falkirk a second goal, the former Peterhead man somehow getting a foot in to block Lyle Taylor, who looked to be clean through on goal.
Airdrie pulled level in 66 minutes when Nathan Blockley chased a long ball into the box and managed to hook it across goal for Alan Cook to slide in and score.
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