Harlequins reached their first Aviva Premiership final with a nail-biting 25-23 victory over Northampton, sealed four minutes from time when Joe Marler was driven over for a converted try.
Just 10 minutes earlier, Northampton appeared to have the game in the bag after Lee Dickson had finished off a 50-metre attack to put the Saints 23-15 ahead.
But Ryan Lamb, who kicked everything else all day, missed with his conversion attempt and that left the door ajar for Harlequins - and it was their pack who barged it open.
Nick Evans' sixth penalty took them within striking distance and then, with 76 minutes on the clock, Harlequins captain Chris Robshaw instructed his fly-half to kick the next penalty to touch.
And from the edge of the Northampton 22, the Harlequins pack launched a ferocious lineout drive with Marler touching down in a forest of legs.
Quins had not only driven Saints over their own line but also infield, leaving the victory conversion a formality for Evans.
It was heartbreaking on the day for Northampton, but over the course of the season Harlequins deserve a place in the final having led the Premiership since September 17.
Conor O'Shea's men will face Leicester across the A316 at Twickenham on May 26.