Mossley allowed the points to slip from their grasp in Monday's Bank Holiday 'derby' defeat at neighbours Droylsden.
Despite the stifling heat the game opened at a good tempo and it was the Lilywhites who had the first chance when Droylsden keeper Thompson did well to turn Adam Morgan's goal bound free kick around the post.
Mossley looked the likelier scorer and so it proved on 20 minutes when Morgan's flicked pass set up Ben Halfacre who hit a superb 20 yard angled left foot volley that nestled in the far top corner of the net.
Mossley looked in comfortable control despite a lack of chances as defenses generally dominated but Mossley were rocked on 38 minutes when Bloods skipper Domaine Rouse hit a 20 yard daisy cutter into the bottom corner beyond Forth's dive after Mossley had failed to clear a Droylsden set piece.
After the break both sides huffed and puffed in the bright sunshine but with few scoring chances for either team, but it was the home side who broke the second half deadlock.
Adam Jones pulled back Aaron Burns for a Droylsden free kick just outside the angle of the box and home substitute Steve Rigby somehow beat Forth with the set piece at the near post despite the Mossley keeper getting full hands to the ball. Rigby could scarce believe his good fortune.
Mossley piled on late pressure on the Droylsden goal but barring Thompson making near post save from Andy Keogh's flicked header the Lilywhites failed to test the home keeper in what in the end was a disappointing performance by Mossley and a first defeat of the new season.