The lead changed hands six times during the 80 minutes as Warlingham secured promotion in Saturday's 20-16 success at closest rivals Old Wellingtonians.
James Agate, with the howling wind and rain at his back, opened the scoring for the visitors the first penalty after a few minutes,
But Old Wellingtonians were soon in front with a try from a well-controlled maul, although the conversion was missed.
Referee Ian McGraw then produced a yellow card to Warlingham lock Ky Oliviera for persistently offending.
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Despite losing their talisman for 10 minutes, Warlingham exerted pressure in the Wellingtonian half with telling breaks from Sam Salter, Dave Stamp and their Australian centre Charles Curry.
Wellingtonians stepped offside and 19-year-old Agate showed nerves of steel with a coolly taken penalty for Warlingham to regain the lead.
The score remained unchanged at 6-5 to the visitors until half-time, but Warlingham's 300 supporters who had travelled to the game were nervous about the role that the windy conditions could play in the second half.
Crucially, a penalty to Wellingtonians early in the second half went wide, but a wayward kick out of defence from Warlingham gave Wellingtonians the opportunity to score a try in the corner. Again, the conversion was missed.
The home back line looked dangerous every time they swept across the pitch, but Warlingham's tackling, especially from captain Tom Street and prop Alex Nunn, held firm.
Their lack of penetration frustrated Wellingtonians and, when they had a man sin-binned, Agate added a third penalty to bring Warlingham back to within a point.
Wellingtonians stretched their lead with their first penalty. However, Warlingham yet again showed their resilience and doggedly marched their hosts back up the pitch with charges from prop Tony Williams and No8 Neil Robson.
Outside half Alex Glover showed his usual sparkling play to move Warlingham deep into the Wellingtonian half, and quickly recycled ball to Dan Street gave the hooker the chance to make a decisive pass for his brother Tom to score a try to put the visitors ahead, with the clock ticking towards the final whistle.
Under pressure, Wellingtonians now used their field position and go for a drop kick, which their outside half deftly placed through the posts.
Warlingham were not to be outdone and once again, Robson drove deep into Wellingtonian territory. Ollie Doe saw his first attempt at a penalty kick bounce off the top of the posts, but another controversial offside decision from Mr McGraw gave him a second chance into the ferocious wind.
Doe needed assistance for the ball to be held steady whilst he took the kick but held his nerve to put the visitors one point ahead.
Substitutes John Delderfield and Mike Cartledge came on for the Crest Nicholson-sponsored Warlingham and Doe put his side further ahead with another well-struck penalty into the wintry wind. With only a couple of minutes left, Wellingtonians kicked to within five metres of the Warlingham line.
They looked very likely to snatch victory, but a try-saving tackle from Tom Street denied the hosts, but came at a cost: Street was forced to leave the field with an elbow injury just before the final whistle blew for a famous Warlingham victory.
"We always knew that, at their ground, Old Wellingtonians would be the most difficult game of the season," Warlingham's playing chairman Anthony Barrington-Doe said.
"It came down to which team wanted the result most and I think we just shaved it there."
Upon their return to their Hamsey Green clubhouse all the Warlingham players lined up to thank their legions of supporters who have always outnumbered the opposition support at every home and away game.
Coach Crammond is already looking forward to the challenges of next season. "London 3 is a good level for committed players, and we should attract some more players, which will help. This season, we have used only 23 players, which of itself is remarkable given the intensity of some of the games we have had.
"We should have gone up last year, but it has been a different matter this season, this division has been a lot tougher - Wellingtonians and London South Africans could both do well in the division above.
"Promotion also raises the prospect of us meeting Purley John Fisher next season, which I know a lot of people in the club will be excited about."
Warlingham still have to play Gosport and Fareham on April 12, but with a four-point lead in the league, they cannot be overtaken.
Wellingtonians could still be promoted if they beat London South Africa and finish in second place to Warlingham.
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