Coughlin on a high at tactics.
Paul Quinn struck in either half before Pat Scullion added a third.
Coughlin said: "I changed the team to add height to combat Forfar's direct style and it gave us a platform to build on."
Scott Dalziel teed up Quinn to fire in the opener after only three minutes.
Dalziel again fed Quinn to sidefoot in No.2 after 69 minutes and set up Scullion to drill in No.3. Forfar's Paul Lunan was shown a straight red for a lunge on Kevin Motion and boss Dick Campbell said: "We were a disgrace - we left our overalls in the house this afternoon."
Quinn: Bagged double