Dunfermline lost ground at the top of Division One and their unbeaten home record as Morton claimed a 3-1 win at East End Park.
David Lyle set Morton on the way after just 35 seconds, scoring from close range.
Both sides then had chances before the away side got the crucial second goal three minutes after the break, David O'Brien converting from six yards.
Alex Keddie almost pulled a goal back for the home side after 65 minutes but he nodded over.
They did get on the scoresheet 13 minutes from time when Joe Cardle fed Liam Buchanan, who easily converted.
However, Peter Weatherston made the game safe for the Ton after 88 minutes, netting his fifth of the season from 12 yards.
Source: DSG
Source: DSG