Lewes are just one game away from playing in the Conference South next season.
The Rooks came from behind to beat premier division side Basingstoke at the Camrose last night in their second promotion play-off.
Craig McAllister put the home side ahead on 27 minutes, but Danny Davis equalised just before half-time.
Lee Newman and Peter Adeniyi put Rooks in control after the break and Davis capped a superb team performance six minutes from time.
Both sides ended the game with ten men after Barry Moore and Neville Roach were sent off five minutes from time.
Lewes now face Kingstonian away on Saturday for the chance to bypass the Isthmian premier division and take a place in the new restructured Conference South.
Manager Steven King said: "The boys were magnificent and we're all in dreamland.
"I was confident we could win but I didn't think it would be that easy.
"All Basingstoke had was the long ball up to their big striker, which made it easy for us because we defended like men possessed."
Lewes were playing their third game in five days. They won the Ryman division one south title with a 2-2 draw against Banstead last Saturday and beat division one north champions, Yeading 1-0 in the first play-off game on Monday.
King added: "We seem to be able to raise our game against whoever we play. There were tired legs out there, but the players didn't let that affect them and we just seemed to get better and better.
"We showed great character to come from behind and it wouldn't have been an injustice if we had won by even more."
King had done his homework on Basingstoke, who had missed out on qualifying automatically for the Conference south after finishing 14th in the premier division.
He knew virtually every player, either personally or through his contacts, and had pin-pointed the defence as their weakness before the game.
Basingstoke were hammered 5-0 at home by Sutton on Saturday and had won just three of their last eight league games.
Lewes, with 114 goals scored this season, needed no invitation to attack. They dominated the early stages and twice went close to taking the lead in the first six minutes.
Joe Vines headed just past the angle of post and bar from a Davis corner. Marc Whiteman then flicked a header wide after a good run and cross by strike partner Newman.
Lewes have been far from convincing at the back themselves this season and it was a defensive error, combined with a stroke of luck, that allowed Basingstoke to open the scoring against the run of play on 27 minutes.
Top-scorer McAllister was allowed to walk through the Lewes defence and when a challenge finally came from Rooks' keeper, Dominique Jean-Zepherin, the ball rebounded off the striker's shin, leaving him with the simple task of tapping into an empty net.
Despite the setback, Lewes continued to press and were rewarded on the stroke of half-time.
Dwain Clarke squared to Davis, who took a touch before slipping the ball neatly under home keeper Scott Tarr with the outside of his foot.
The Rooks killed the game off with two goals in the first six minutes of the second half.
Newman showed great technique to volley under Tarr from six yards after Mark Patterson had made a mess of an attempted headed clearance.
Adeniyi left the home supporters shell-shocked moments later when he took a cut-back by Newman in his stride and curled a left foot shot from just inside the area into the bottom corner.
Davis ended any hopes the home side had of a comeback six minutes from time when Tarr blasted a clearance against his legs and the ball ran into the gaping goal.
Lewes's evening was tainted slightly on 85 minutes when Moore was given a straight red card for retaliating to a punch from Roach, who was also sent off.
Kingstonian reached Saturday's showdown by winning 4-2 on penalties at Harrow Borough last night after the sides had shared a 0-0 draw.
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