Dale Hilson and Chris Templeman were on target as Forfar edged past fellow League One strugglers East Fife 2-1 to take their place in the fourth round.
Robert Douglas parried Liam Buchanan's early effort as the two sides cancelled each other out for the majority of the first period.
But on the stroke of half-time Hilson gave the hosts the lead, firing into the bottom corner after good work from Marvin Andrews.
Templeman doubled the lead in the 69th minute, forcing the ball over the line after East Fife had failed to clear a corner.
Craig Johnstone pulled a goal back five minutes later when he collected Stephen Hughes' pass and fired in from close range.
But the visitors were unable to force a leveller to take the tie to a replay.