Carlos Bocanegra and Maurice Edu also each grabbed a goal as the Scottish champions responded positively to the midweek defeat by the Irn-Bru First Division side.
Victory at East End Park allowed SPL leaders Rangers to pile further pressure on Celtic, and was also the perfect 49th birthday present for manager Ally McCoist.
Rangers made four changes to the side that crashed out of the cup, with goalkeeper Allan McGregor, Edu, Naismith and Nikica Jelavic all drafted in as McCoist named the team that defeated Celtic in last week's Old Firm derby.
Young midfielder Rhys McCabe was named on the bench for the first time, while the Pars made just one change as Andy Barrowman started ahead of Andy Kirk.
Rangers had the chance to pile on some early pressure when Kyle Lafferty won a free-kick 25 yards out.
Gregg Wylde sent a swerving effort into the box and was only denied the opener by a decent save from goalkeeper Paul Gallacher, who reacted quickly to push the set-piece past his left-hand post.
But he was left picking the ball out of the back of the net with just eight minutes gone when Rangers took the lead from the resultant corner. Steven Davis picked out Bocanegra who connected well to nod past Gallacher and claim his first SPL goal for the club.
Rangers doubled their advantage after 17 minutes when Edu collected a short pass from Jelavic and sent an impressive strike past the helpless Gallacher from 20 yards.
Rangers continued to push forward in search of more goals and Naismith was not too far away with a shot that fizzed narrowly wide.
At the other end, Dunfermline carved out their first real chance when Gary Mason's cross was met by Ryan Thomson and his header was touched just over by McGregor at full stretch.
There was concern for Rangers when Dorin Goian went down injured during the build-up to that chance and left the pitch on a stretcher before returning to the action following treatment on the sidelines.
Rangers could have added to their lead when Jelavic set up Davis but his poor header fell wide of target, before Wylde tested Gallacher with an effort that the goalkeeper initially spilled before recovering to smother.
Dunfermline's hopes of a comeback in the second half were dealt a blow when Rangers found the back of the net again just six minutes after the restart.
Naismith raced onto a pass from Davis and kept his cool to stroke past Gallacher from 12 yards, before Steven Whittaker went within inches of adding his name to the scoresheet with a well-struck shot from long distance that dipped but went just over the crossbar.
Dunfermline could have pulled a goal back when David Graham found himself with only McGregor to beat but the goalkeeper was up to the task with an impressive block.
It was proving to be a busy afternoon for Gallacher who was called into action to force a Jelavic free-kick over, before denying a ferocious effort from Whittaker.
But he was unable to prevent Naismith from claiming his second of the day with nine minutes remaining.
Davis went on a great run before finding Jelavic, who whipped the ball across the face of goal for Naismith to rifle home from close range.