Second-placed Eastbourne Town failed to take advantage, losing 3-1 at home to St Leonards despite going ahead through Gary Brockwell.
Sean Ray drilled a shot into the far corner to level and Michael Morgan edged Saints ahead.
Tim Olorunda produced a tricky turn to settle the contest, in which each team had a man dismissed.
East Preston are up to second and eyeing a title challenge after their 3-0 success at Selsey.
Chris Hibberd and Matt Huckett put them in charge before Andy McCarthy saved a penalty to maintain the two-goal cushion. Lee Farrell hit the third.
Boss Vic Short said: "We're happy with a cleansheet and three goals and the other two losing makes it even sweeter."
Hassocks missed the chance to close on the leaders as they drew 4-4 at rock-bottom Shoreham but boss Dave John admitted: "We were never going to win the league anyway."
They were relieved to even get a point as James Laing completed a trio of close-range finishes with the equaliser seven minutes into stoppage time. Shoreham took charge as Paul Ettridge and a thumping Martin O'Donnell finish sent them two-up.
Joe Fernley replied with a belter but sharp work by Chris Pearson led to a penalty from which Darren Annis coolly stroked Shoreham into a 3-1 lead.
Laing dragged Robins level but Shoreham were back in front going into stoppage time as Annis flicked the ball on and Chris Koffe finished with Hassocks claiming offside.
John added: "It was pantomime season for us defensively."
East Grinstead continue to improve, their 3-2 success at Horsham YMCA making it seven wins out of eight.
Adam Simpson scored twice and there was also a well-worked finish by James Horner.
Steve Davies and Phil Churchill were on target for YM.
Manager Ian Dawes was stunned to see the referee abandon Redhill's match at Three Bridges at half time due to floodlight failure.
Boss Dawes, who watched Bronek Dearowa score the only goal of the half for his side, said: "The referee came in at half time and told us he was abandoning the game because the floodlights had frozen and couldn't be turned round.
"He explained that it could only be done manually which would take more than half an hour and so he just called it a day."
A late John O'Donoghue goal earned Southwick all three points at Ringmer. The striker netted with ten minutes to go when he worked himself into space and fired in from 18 yards.
Rye and Iden United shared the points with visiting Sidley. The home side's Scott Price missed a penalty on the hour thanks to a superb Rob Wiley save before Sidley took the lead on 78 minutes through Adam Day. Another penalty ensured Rye a point when Shaun Loft converted.
Hailsham Town joint-boss Steve Latuske was delighted with his side's start to 2004 as they beat Whitehawk 3-0.
Sidlesham came away from Pagham with a 3-0 win. Scott Tipper scored the first after 50 seconds but his side had to wait until after the break for their second. Richie Davies was on target before substitute Joe Leggett added a third.
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