Leinster escaped the Twickenham Stoop with an unlikely 6-5 victory to set up an all-Irish Heineken Cup semi-final against fierce rivals Munster at Croke Park.
Brian O’Driscoll’s side, containing five of Ireland’s Grand Slam heroes, were battered relentlessly but prevailed thanks to two penalties by Felipe Contepomi.
Points may have been at a premium - Leinster led 6-0 until the 66th minute - but it was a gripping contest played with brutal intensity.
The Irish province, semi-finalists on three previous occasions, moved through the gears in the third quarter but with 20 minutes to go Quins were back on the offensive.
England full-back Mike Brown dashed over but substitute fly-half Chris Malone, on for injured former All Black Nick Evans, missed the conversion.
Evans reappeared as a blood replacement for Tom Williams in a move that angered Leinster’s dug-out but the Kiwi failed with a late drop-goal attempt.