Harlequins defied their dismal domestic form to avenge their 2009 'Bloodgate' defeat by Leinster and continue their flawless passage through the group phase of the inaugural Champions Cup with a 24-18 win at The Stoop.
The third quarter delivered the turning point when outstanding number eight Nick Easter touched down with outstretched arms in a magnificent finish to break the 9-9 half-time deadlock.
Five minutes later wing Aseli Tikoirotuma then breached the three-times European champions with a 70-metre intercept try as Quins cemented their place at the summit of Pool Two ahead of Saturday's return trip to Dublin.
Two late penalties from Ian Madigan set up a tense final 10 minutes, but scrum-half Danny Care calmed nerves by landing a late drop-goal in an impressive finish from a club languishing ninth in the Aviva Premiership.
Eleven players from the only previous meeting between the rivals in April 2009 were on display at Twickenham Stoop, six from Quins and four from Leinster with prop Mike Ross having represented different clubs in each game.
Ross endured a torrid afternoon at Twickenham Stoop after being demolished by Joe Marler in the scrum, and there were also notable performances from Marler's fellow England internationals Chris Robshaw and Care.
The dominant scrum will have been welcomed by Conor O'Shea, who saw his pack pulverised at the set piece by Bath last weekend.
Quins were clearly fired-up at the end of a week that saw minds drift back to the episode in the Heineken Cup quarter-final five and a half years ago when a faked blood injury dragged the reputation of the game through the mud and resulted in a three-year ban for then director of rugby Dean Richards.
Madigan and Evans swapped early penalties, but the opening was notable for the visiting scrum being driven into the turf, loosehead Jack McGrath proving the weak link on this occasion.
Easter gave opposite number Jamie Heaslip a pat on the back in mock commiseration after the Leinster scrum was demolished once more and the nightmare continued when Ross was driven into the turf.
Evans limped off with a groin injury and his replacement Tim Swiel landed three points, but Quins were struggling to capitalise on their set piece dominance with their Irish opponents forcing small openings with fly-half Jimmy Gopperth lively.
Madigan and Swiel exchanged penalties, the second of which came after a strong attack launched by a turnover from the omnipresent Robshaw, who was then prominent in a bright start to the second half.
Care escaped on a smart run and the England contingent were to the fore as Leinster's defence was tested with Marler subduing Ross once more, Robshaw acting as the link-man in open play and Mike Brown probing down the flanks.
The pressure finally created an opening with Marland Yarde being stopped short of the line moments before Easter produced his sublime finish with Swiel converting.
Disaster struck for Leinster for a second time as they created an opening just metres short of the whitewash only for Kearney's final pass to Zane Kirchner to be picked off by Aseli Tikoirotuma who then crossed after a 70-metre sprint to the line.
Madigan slotted successive penalties to narrow the deficit to six points, but Care's drop-goal put Quins back in thee driving seat.