Warlingham went to top-of-the-table Crowborough and turned the form book on its head, running out 29-16 winners.
More impressively, it was the first time the London Division Two South East leaders have been turned over at their fortress home in 18 months.
The driving force behind Warlingham's triumph was Mark Kozminski who kicked five penalties on his way to a 19-point haul.
Warlingham captain Zack King said: "That was the toughest game yet this season, but to get the win here is immense.
"All the lads put everything into this one and will feel it tomorrow."
Both sides exchanged penalties until Warlingham were awarded a penalty try and found themselves 10-3 ahead at the break.
On the resumption, Warlingham extended their lead when Jon Osborne intercepted a speculative pass and outstripped the defence to score a converted try.
Another long range artillery shot from Kozminski put clear water between the teams and Crowborough were forced to play catch-up rugby - something new to them.
Crowborough responded with a scrambled try in the corner, but Kozminski pegged them back again with another brace of penalties.
For a while Warlingham found themselves on the rack, but the defence, especially centre Luke Davies and full back Joe McEvoy, were unforgiving, and bone shuddering tackles from Bradley Saffery and Alex Skinner stopped the attacks.
Crowborough eventually cracked open the Warlingham defence and scored again in the corner.
The penalty count against them was the difference and when Warlingham were awarded yet another penalty late into the game, the match was won - but not before Kozminski added insult to injury by kicking his, and Waringham's final points on the final whistle.
This weekend, Warlingham host Medway in the league, and they and have drawn away at Thanet in the second round of the RFU Intermediate Cup in November.