Horsham’s Premier Division lead was narrowed to just 18 points ahead of Cuckfield in second place after they suffered a five-wicket defeat at the hands of East Grinstead.
The Lions lost the toss and were asked to bat and lost wickets regularly as the Grinstead attack shared the spoils between them at the Saint Hill Ground.
Joe Ludlow made 27, Tom Johnson hit 29 and Michael Thornely 23 but no-one could stay in long enough to build a big innings.
Horsham were all out for just 111 in 27.5 overs as Grinstead bowlers Lewis Hatchett (2-25), Ian Sturmer (2-51), Will Adkin (2-27) and Bradley Hatchett (4-3) shared the wickets.
Grinstead then made easy work of overtaking their target with Regan Derham, 20, leading the way by hitting 60 off 85 balls.
Lewis Hatchett added 23 further down the order as they reached 114-5 to win in 26.4 overs and collected maximum points while Horsham took just two points.
Sam Cushing was the visitors’ most-successful bowler, taking 3-23 to help send Horsham home in an earlier-than expected 5pm finish.
Horsham captain James Johnson said: “Saturday was very disappointing. It was just one of those things that everyone plays once a season.
“It’s the only time it has happened this season.
“The pitch was pretty tough to bat on but that wasn’t an excuse for the way we played.
“I think because we have been playing so well we took the foot off the gas and were slightly careless.
“It might do us some good, a result we can work on and make sure we don’t play like that again.
“111 was never going to be enough, especially against the likes of East Grinstead.
“The batting was at fault for the first time this season.
“At the start of the season we spoke about people being responsible, but no-one really stuck their hand up.
“We had our backs up against the wall. It was a pretty tough pitch to bat on.
“Most of their bowlers were dangerous. Bradley Hatchett took most of their wickets but we were pretty careless when we faced him.
“The pitch did spin quite a bit, but it wasn’t anything to be frightened of.
“You’d be lying if you said you would go through the season without a blip.
“I just hope it’s the only one and we give a much better display this weekend at Brighton and Hove.
“The Nevill Sports Ground is not the most inviting place to go to, so it’s about us getting the team right and collecting as many points as possible.”
Horsham will be without their opening batsman Ludlow who is away on holiday.
Tom Haines could feature having finished his schooling for the summer.