Horsham YMCA lost more ground in the Premier Division title race as they suffered a shock home defeat to strugglers Shoreham on Saturday afternoon.
The Mussels ended a nine-game winless run in the league under new manager Curtis Foster, who was taking charge from the first time since switching from Worthing United last week.
Thomas Johnston's second-half strike was the difference between the two sides at Gorings Mead in a match that had a distinct lack of quality in the final third.
Second-placed YM controlled the first half although struggled to carve out clear-cut chances, before the visitors, who defended stoutly throughout, grew into the game after the break.
The hosts had the first and one of the best chances of the first half after ten minutes as Adam Hunt played a defence-splitting pass behind the Shoreham backline and Tony Nwachukwu raced onto the ball and put a low cross in for Dean Bown, who turned wide under pressure.
Just a minute later, Jay Carse broke forward and space opened up for the midfielder, but he shot tamely at Aaron Jeal. Back at the other end, Nwachwukwu delivered a teasing ball across goal, but no-one could connect.
George Olulode drove forwards trying to get Shoreham on the front foot with a good run, but his dangerous pass in the final third was cut-out well by Dan Evans.
Jay Carse's game was cut short in the 22nd minute when he collided with Nwachukwu and both went down, but the Shoreham man came off worse and was replaced by Myles Goatley.
Nwachukwu then headed Alex Barbary's cross straight at James Broadbent, before Luke Gedling fired just over from the edge of the box after another good run from Barbary across the box.
Shoreham came out with more attacking intent in the second half and Luke Usherwood and Alfie Proto-Gates had a couple of early probing runs that were dealt with well by Evans and Callum Donaghey.
YM continued in struggling to find the final pass or bit of quality in the final third, while Shoreham's John Rhodie forced a good diving save from Jeal, who pushed the ball around the post.
On 65 minutes, a sloppy back pass put Goatley in one-on-one with Jeal, but the goalkeeper stood tall and caught a tame effort from the Shoreham player.
Johnston then saw a deflected shot drop narrowly wide in a counter-attack breakaway after Evans carelessly lost the ball on the edge of the Shoreham box.
YM were not so fortunate moments later when Shoreham broke again. The ball was shifted in to Johnston, who was allowed time and space in the box to set himself and finish low into the far corner.
The hosts responded with a flashed shot that Broadbent saved well and put Donaghey up front with Jack Harley also coming off the bench.
Things became desperate with YM realizing the importance of not dropping points, but they failed to break down a stubborn Shoreham backline.
Bown showed some neat skill to take a low cross, cut back, nutmeg a defender, but then fired high and wide. Gedling fired a dangerous free kick across goal and Evans put another glancing header just wide from another set-piece.
As the clock ticked down, YM had a late spell of constant pressure from free kicks and corner which resulted in Jeal coming up to join the attack, but Shoreham saw out the pressure and held on for a rare three points.
The result sees YM slip to third in the table with Newhaven, who won 4-0 at Langney Wanderers, leapfrogging them in the table and leaders Chichester City extending the gap at the top with their 2-0 win at Loxwood.
Horsham: Jeal, Carden, Harding, Donaghey, Evans, Nwachukwu (Eales 78), Gedling, Hunt (Mobsby 60), Barbary (Hartley 67), Garrod, Bown. Unused: Frankland, Dugdale.
Shoreham: Broadbent, Firman, Dunk, Denyer, Bromage, Olilode, Rhodie (Collier 85), J.Carse (Goatley 22), Proto-Gates, Usherwood (McCormick 78), Johnston. Unused: Kirk-Patrick, R.Carse.