Crawley Down slipped two places to sixth after suffering a frustrating home defeat against an improved Merstham side.
Fabio Saraiva tapped in the only goal of a game for the visitors in the 63rd minute.
The Anvils had a golden opportunity to equalise 12 minutes before the final whistle when Jamie Cade was brought down in the area and then saw his own penalty kick saved by Oshane Brown.
Merstham’s Saraiva announced his intention with an early attempt on goal which was caught by keeper Tony Di Bernardo.
At the other end, Fraser Logan had a piledriver blocked by the defence before Cade lifted the follow-up shot over the bar.
Down suffered an early blow after half an hour when right back Charlie Slocombe left the field with a recurrence of a hamstring injury and was replaced by Tom Graves.
In a half lacking in clear-cut chances, Down came closest to scoring when Logan found the net, only to have the goal ruled out for offside.
Joe Holland showed some step-over skills before launching a powerful strike for Merstham which was tipped over the bar by Di Bernardo.
Down then pressurised the visitors’ area with a series of four successive corners, none of which led to a goalscoring opportunity.
After the break Di Barnardo twice pulled off saves to deny Merstham, once from Holland and once from Lee Newman before the visitors took the lead.
Saraiva was left unmarked a few yards from goal annd made it look easy as he put away having been set-up by a cross from Newman.
Down didn’t create that much in the second half but should surely have made the most of a penalty by Cade was saved by Brown after Cade had been awarded the controversial spot-kick after being fouled in the area by Justin Hemmings, who was also booked.
In the final moments Ross Morley had the ball grabbed from his feet by Brown before he could shoot and at the home end, substitute Adam Moriarty crossed for Saraiva to have a go and the on-target effort was kept out by Di Bernardo as the Anvils were beaten for the second time in five matches.
Crawley Down Gatwick: Di Brnardo, Slocombe (Graves 30), Geard, Richards, Page, Morley, Odunaike, Sargent, Cade, Blewden, Logan.
Unused subs: Bold, Bingham, T Frankland, R Frankland
Man of the Match: Matt Geard