Forfar ran riot against a poor Dumbarton defence. The home side seemed able to score at will and the result allowed them to leapfrog Dumbarton in the battle against relegation.
Paul Shields was the hero for Forfar with his second hat-trick of the season.
He opened his account in the 41st minute when he stuck out a leg to turn the ball home, despite being surrounded by defenders. Two minutes later he doubled Forfar's lead with a clever lob over keeper Stephen Grindlay from just outside the box.
Forfar picked up the pace after the interval, and Shields turned provider in the 51st minute when he crossed from the right to give Mathu King, M an easy tap-in.
Shields completed his hat-trick in the 57th minute when he stole the ball from Robert Walker and rounded the keeper to roll into an empty net.
David McClune made it five in the 64th minute when he hammered home from six yards, and Paul Tosh completed the rout in the 72nd minute with his first touch of the ball after coming on as a substitute.
Dumbarton must have been left wondering what might have been had a James McKinstry free-kick not come back off the post when the score was still 0-0.