ASCOT United lost 1-0 away to Southall with their former striker, Dave Pitt, netting the winner.
It was their third defeat in a row and their lead at the top of the Premier Division has been reduced to one point.
The Yellamen had goalie Sam Gray to thank for keeping them on level terms at half-time, but they started the second half on the front foot with Ian Davies going close and Usman Lalustani seeing his effort blocked.
Southall sent on Pitt with an hour gone and he caused Ascot a few problems before hitting the winner 15 minutes from time, cracking an unstoppable effort high into the top right-hand corner.
Lalustani missed a chance to equalise, but it needed an excellent save from Gray to deny Pitt a late second goal.
United host third-placed Abbey Rangers this Saturday before visiting Badshot Lea next Tuesday (7.30pm).
Ascot have been drawn at home to Southern League side Beaconsfield Town in the first round of the Berks & Bucks Senior Cup, with the tie expected to go ahead on Tuesday, November 5.
Eversley & California lost 3-1 at Cove to leave them bottom of the Division One standings with four points from 10 games.
Poor defending led to Kieran Rodgers opening the scoring on 10 minutes.
Josh Francis equalised after 25 minutes, only for Rodgers to restore Cove's lead five minutes before half-time.
Boars were unlucky to be trailing at the break, but they failed to lift their game in the second half and a foul by Jamie Griggs enabled Rodgers to complete his hat-trick from the penalty spot.
Eversley, whose Division One Cup tie away to Kensington & Ealing Borough last Tuesday was postponed, are home to Bedfont & Feltham this Saturday.
Sandhurst Town were beaten 2-1 at home by Dorking Wanderers Reserves, whose goals came from James Dickson and Javin Dougan.
Fizzers have added to their squad by signing keeper Andy Rider from Sheerwater, and midfielder James Pilgrim, who is returning to football after having a short break.
They were due to host Chessington & Hook United in the Division One Cup last night (Tuesday) and will be home again in the league this Saturday when second-bottom Bagshot are the visitors.
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