Harlequins outscored Saracens three tries to one to claim a crucial 24-19 victory at a packed Wembley Stadium on Saturday.
A record-breaking crowd saw Harlequins hold off a late Saracens fightback to maitain top stop in the Aviva Premiership standings.
It didn't take Harlequins long to break the deadlock, taking the lead in the 3rd minute courtesy of a Jordan Turner-Hall try, which was converted by Nick Evans.
But Quins' indiscipline would cost them their early advantage, as three Owen Farrell penalties in nine minutes turned the score line on its head and handed Sarries a narrow lead.
The ding-dong battle went up another gear just after the end of the first quarter as George Lowe put Quins back in front with a well-taken try. Nick Evans' second conversion made it 14-9.
The huge Wembley crowd were lapping up the entertainment on offer but they'd have to wait more than half an hour to see the game's next try.
Farrell's fourth penalty on the stroke of half-time shaved three points off Quins' advantage, but the Premiership pace-setters were dominant during a pivotal opening 20 minutes following the restart.
Rory Clegg's penalty on 45 minutes stretched Harelquins lead back out to five, before Danny Care crossed for a crucial try, converted by Clegg, just before the hour.
There was still time for Saracens to stage a fightback, however, and, after Joe Marler and Danny Care were sent to the sin-bin, Richard Wigglesworth's converted try set up a grandstand finish.
With Harlequins down to 14 men for the final ten minutes, Sarries rallied forward in search of a crucial second try.
Clegg wasted the opportunity to boot his side to safety, and the leaders lost a third player, Nick Easter, to the sin-bin, but it mattered little in the end as Harlequins held on for the win.
Pens: Farrell 3
Tries: Turner-Hall, Lowe, Care
Cons: Evans 2, Clegg
Yellow cards: Marler (Quins - 62nd min); Care (Quins - 70th min); Easter (Quins - 79th min)
Saracens: 15 Alex Goode, 14 David Strettle, 13 Chris Wyles, 12 Owen Farrell, 11 James Short, 10 Charlie Hodgson, 9 Neil de Kock, 8 Ernst Joubert, 7 Will Fraser, 6 Justin Melck, 5 Mouritz Botha, 4 Steve Borthwick (c), 3 Carlos Nieto, 2 Schalk Brits, 1 Matt Stevens.
Replacements: 16 Jamie George, 17 Mako Vunipola, 18 Petrus du Plessis, 19 George Kruis, 20 Jackson Wray, 21 Richard Wigglesworth, 22 Adam Powell, 23 Michael Tagicakibau.
Harlequins: 15 Mike Brown, 14 Tom Williams, 13 George Lowe, 12 Jordan Turner-Hall, 11 Ugo Monye, 10 Nick Evans,9 Danny Care, 8 Nick Easter, 7 Chris Robshaw (c), 6 Maurie Fa'asavalu, 5 George Robson, 4 Ollie Kohn, 3 James Johnston, 2 Rob Buchanan, 1 Joe Marler
Replacements: 16 Aston Croall, 17 Mark Lambert, 18 Will Collier, 19 Tomas Vallejos, 20 Tom Guest, 21 Karl Dickson, 22 Rory Clegg, 23 Ross Chisholm.
Venue: Wembley Stadium
Referee: Referee: Greg Garner