Letchworth turned the promotion and title race on its head in London Two North West with a determined victory over the leaders.
The Honourable Artillery Company arrived at Legends Lane with 15 wins from 15 games but returned on the end of an 8-7 loss following a titanic effort from the home side.
The result leaves Letchworth in third, five points behind new leaders Old Priorians, who jumped above HAC courtesy of a 45-19 success at home to Grasshoppers.
That potential promotion decider with the east London club is scheduled for the final day of the season in April.
The former pacesetters are now just three points above the Legends although they have played a game less.
This was a pulsating and somewhat brutal match played in front of a large crowd. Although never dirty, some of the hits did make the watching public wince.
Letchworth had a strong wind behind them in the first half but it was the HAC backs who exploited their running game with more fluidity and opened the scoring when their outstanding fly-half Jack Polson inspired an 80-metre try which was converted.
The hosts refused to buckle though and could have crossed the whitewash themselves on a number of occasions.
The one crucial moment though came when Hem Johal opted to go for the posts instead of the corner, slotting the penalty to make it 7-3 at the interval.
With the wind now in their faces, Letchworth played superbly and took the game to HAC.
After several sizzling runs by the Johals, Aman and Arun, as well as Daniel Odita and Tatenda Gurure, it was then the forwards turn to batter the visitors line with Scott Quarmby, Martin Day, Conor Turner, Kyle Hughes and man of the match Joe Allison to the fore.
The eventual match winner though was Oscar Robinson who dived over to give the home sides the narrowest of margins that, with the crowd now in full vocal flow, they never lost.
Letchworth kept out the visitors with steel and discipline, even surviving 10 minutes with 14 men after Hughes was yellow carded.
The strength of the wind also meant penalties were kickable anywhere in the Letchworth half but their discipline remained throughout and the relief and exhilaration at the final whistle proved what a big win this was.
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