Burgess Hill suffered their first taste of defeat since September last year.
Danny Hinshelwood's Selsey won 2-1 at the High Street Ground to bag a place in the semi-finals of the RUR Cup.
The Hillians have not lost a game since a 3-1 reverse after extra time against Tooting and Mitcham in the FA Cup way back on September 4 but Selsey put an end to that proud record to leave the player-manager purring.
Hinshelwood said: "There will be a few people rubbing their eyes at this result.
"It was a good game played at a high tempo. We showed we are a side to be reckoned with on our day and it is just a case of finding consistency."
It looked like business as usual when Phil Churchill gave the Hillians the lead after 24 minutes but good work by Lee Stevens forged an opening for Paul Lee to level from six yards out on 38 minutes. Clinton More, on loan from Eastbourne Borough, grabbed the winning goal from a cross just before half-time.
Selsey were indebted to goalkeeper David Leaver in the latter stages as he made two great saves from Churchill to ensure the hosts' safe passage.
With the Hillians in cup action and Sidley's game at Withdean postponed, Three Bridges had the chance to close on the leaders but were held to a 0-0 draw by Joey Stevens' Hailsham.
Hailsham had Matt Smith sent off in the second half for his second bookable offence but Bridges were never able to find the killer goal.
Boss Darren Barker said: "I'm very disappointed. We had 80 per cent of the possession and our build up play was good but we lacked the final effort. It was two points dropped."
Peacehaven eased to a 3-1 lead at half-time against visitors Pagham although they could afford to miss a penalty.
Tommy Pattenden, Joe Kitambie and Ian Costello, from the penalty spot following a push on Owen Hill, got Peacehaven's goals while Pagham levelled through Hammond. Pagham had Chris Rustell sent off in the second half for two bookable offences.
There were a number of surprises in the scrap at the bottom of the table with Sidlesham grabbing a 1-0 win at Ringmer after a strong defensive display. Ringmer's Stuart Corlett was sent off for his second yellow card after the break before Sidlesham substitute Craig Williams' direct free kick decided the outcome.
Southwick also picked up a notable victory over Arundel as they won 4-1 at Old Barn Way with goals from Jack Dineen (2), Wayne Potbury and Toby Hutchinson. Jason Wimbleton replied for the visitors.
Manager Sammy Donnelly said: "It was an encouraging result. The team work and the team's effort were good."
Hassocks continued to pull away from trouble as they beat Littlehampton 4-2 at the Beacon with boss Dave John impressed by their come back from a goal behind.
Steve Wilkins replied after Derren Woods had put the Marigolds ahead and he added a second from an acute angle to put the Robins in front. James Laing got the third before Wilkins was felled for a penalty which Laing converted for the fourth. Shaheen Sadough got the visitors' second in the final minute.
There was no respite for basement side Saltdean as they slipped to a 3-1 defeat at Wick despite producing a battling display.
Gareth Green produced an impressive display for the hosts, scoring the first goal and supplying the cross from which Dave Schneider got the third after Adie Miles had tucked away the second. Brad Dougal got Saltdean's consolation.
Redhill staged a remarkable comeback to draw 4-4 with Eastbourne United after being 4-1 down as manager Bill Tucker's substitutions paid dividends.
David Harris (2), Carl Harris and Ollie Walton netted for United.
But substitutes Paul McKay and Herve King replied and Paul Smith grabbed a last-minute equaliser. Paul Garrett had earlier put Redhill in the lead.
Horsham YMCA's Nick Flint (2) and Ramin Jarvand were on target in a 3-0 win at Chichester City United.
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