Despite being on the receiving end of two yellow cards, Harlequins pulled off a 16-13 upset win over Northampton on Saturday.
The shock result at Franklin's Gardens end the Aviva Premiership leaders' unbeaten home record which stretched back to May last year.
Northampton looked sure-fire winners when they were 10-3 up at half time with the visitors facing the opening 10 minutes of the second half with John Andress and Nick Easter in the bin, but a try from England scrum-half Danny Care and a conversion and two penalties from Nick Evans saw Quins claim an unlikely win.
The Quins had the first scoring opportunity in the third minute but they were unable to take it as an Evans penalty attempt from halfway sailed narrowly wide.
The visitors continued their bright opening with Tom Williams and Easter combining well to get the Quins into the opposition 22. The Saints were penalised but once again Evans missed the penalty chance.
After 10 minutes the Saints had their first period of pressure.
James Downey brushed aside Chris Robshaw's tackle and the home side moved the ball sweetly to send Chris Ashton on a penetrating run down the touchline.
The Quins snuffed out that threat but Northampton maintained the pressure and in fact crossed the line through Downey, but the referee correctly ruled the final pass from Courtney Lawes to be forward.
The Saints continued to have the better of the game in terms of territory and possession but could make little headway against strong tackling defence from the Quins.
But eventually their pressure was rewarded when Stephen Myler gave them the home side the lead in the 26th minute with a simple penalty after the visiting three-quarters were adjudged to be offside.
Northampton's lead was shortlived as Evans replied in kind but back came Saints, and when Evans sliced his clearance kick to allow the hosts a line-out in a good attacking position it was the forerunner to a disastrous five minutes for the Quins.
They were placed under tremendous pressure in the scrum and conceded a succession of penalties. Eventually the referee's patience was exhausted and prop Andress was sent to the sin bin.
The Saints attacked from the next scrum and Easter was forced to concede yet another penalty to prevent a try and was promptly yellow carded to leave Conor O'Shea's side two men down.
The six-man Quins scrum stood no chance at the next engagement and gave away a penalty try, which Myler converted with the last kick of the half to give the Saints a deserved 10-3 interval lead.
Quins did superbly to hold out the Saints for the first 10 minutes of the second half as Andress and Easter returned with no further damage to the scoreline.
Their tenacity was soon rewarded when Care charged down a clearance kick from Myler to collect the ball and score a try which Evans converted to bring Quins level.
With equal numbers the Quins were now able to match the home side and in the 63rd minute they took the lead for the first time when Evans kicked a 20-metre penalty, and that lead was extended when the outside half added another penalty with 12 minutes to go.
Northampton replacement Shane Geraghty reduced the arrears with a penalty but the Quins held on for a famous victory.
Try: Penalty try
Pen: Myler, Geraghty
Pens: Evans 3
Yellow cards: Andress (Harlequins - 39th min); Easter (Harlequins - 40th min)
Northampton: 15 Ben Foden, 14 Chris Ashton, 13 Jon Clarke, 12 James Downey, 11 Paul Diggin, 10 Stephen Myler, 9 Lee Dickson, 8 Roger Wilson, 7 Tom Wood, 6 Phil Dowson, 5 Christian Day, 4 Courtney Lawes, 3 Brian Mujati, 2 Dylan Hartley (capt), 1 Soane Tonga'uiha.
Replacements: 16 Brett Sharman, 17 Regardt Dreyer, 18 Tom Mercey, 19 Mark Sorenson, 20 Calum Clark, 21 Ryan Powell, 22 Shane Geraghty, 23 Joe Ansbro.
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 (capt), 6 Tom Guest, 5 George Robson, 4 Ollie Kohn, 3 James Johnston, 2 Matt Cairns, 1 Joe Marler.
Replacements: 16 Chris Brooker, 17 Mark Lambert, 18 John Andress, 19 Tomas Vallejos, 20 Will Skinner, 21 Karl Dickson, 22 Rory Clegg, 23 Tom Casson.
Venue: Franklin's Gardens
Referee: Dean Richards