Dunfermline were no match for First Division leaders Morton, who ran out 4-1 winners at East End Park.
Doubles for Peter MacDonald and Michael Tidser gave the visitors a four-goal lead with barely an hour played, and Callum Morris' late reply could not prevent a fourth straight home defeat.
Victory maintained a three-point lead at the top for Morton, who are yet to lose a league game on the road this season, and the result was rarely in doubt from the moment of MacDonald's opener.
It came from the penalty spot in the 31st minute after Fouad Bachirou was fouled, and Tidser doubled the lead just after half-time with a 20-yarder from Chris Kane's poor clearance.
Two more followed in short order, a Morton counter-attack ending with MacDonald's header and Tidser driving in a second from a half-cleared corner.
Morris' 83rd-minute header reduced the deficit, but the damage was done.