Horsham slipped to 59 points behind leaders Roffey when they suffered a two-wicket defeat at the hands of Hastings.
The former leaders have now fallen a place to fourth in the table, having won only once in their last five games.
Skipper Michael Thornely took charge of the side in the absence of James Johnson and topscored with 41 off 80 balls and shared in a stand of 69 runs for the fifth wicket with Tom Johnson (28).
Horsham were all out for 147 as the spinners prospered, Jed O’Brien taking 4-50 and Elliot Hooper claiming 2-44, which included the prized wicket of Thornely, bowled out.
Thornely said: “The wicket was used which suited their left arm spinners (O’Brien and Hooper).
“We won the toss and realised quite soon the wicket wasn’t as good as we’d thought it would be.
“175 would have been a really good score.
“We made a nice start but it was difficult to score and we lost three or four wickets quite quickly.
“Me and Tom Johnson put on 35 and we had got out when we were trying to get about 160-170.”
In their reply, Hastings could not deal with Horsham spinner Michael Munday, who took 7-69.
Will Beer, back from Sussex duty, took the only other wicket to fall for 40 runs as Hastings overtook their target in 40.5 overs.
James Pooley topscored with 46 and O’Brien made 30 to help them on to victory.
Thornely added: “James Pooley played perfectly and got them off to a good start. Once Munday and Beer started to bowl we started to pick up wickets.
“Hastings were motivated in the contest. We were about 15-20 runs short with the bat. I said let’s give it everything and it ended up being a very tight finish.
“Michael (Munday) got two wickets from successive balls and had a big shout for a hat-trick which was close and anything could have happened.”
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