Fleetwood enjoyed the better of a lacklustre first half with good chances to break the deadlock.
Sam Finley’s dink over Doncaster keeper Louis Jones forced player-manager Andy Butler to head off the line.
Vassell cut out a slack pass and surged forward before striking the post with a shot from the edge of the box.
Fleetwood took the lead on 51 minutes when Swansea loanee McKay raced in from the left and finished well from a tight angle.
Vassell went close to immediately doubling the advantage when he looked to catch Jones out from a long ball.
The closest Doncaster came to an equaliser was with a Reece James shot that hit the side netting.
Callum Camps should have doubled Fleetwood’s lead but fired wide from close range while Ged Garner drew a good save from Jones as the visitors saw out the win comfortably.
Support The Yorkshire Post and become a subscriber today. Your subscription will help us to continue to bring quality news to the people of Yorkshire. In return, you’ll see fewer ads on site, get free access to our app and receive exclusive members-only offers. Click HERE to subscribe.