Harlequins outscored Leinster two tries to none to win 24-18 in a hard-fought European Champions Cup clash at The Stoop on Saturday.
The scores were locked at 9-all at the interval but tries from man-of-the-match Nick Easter and wing Aseli Tikoirotuma gave Quins the advantage in the second half.
The win means Quins are now three points clear at the top of pool two, and Leinster will be looking over their shoulder at Wasps, who beat Castres earlier in the day.
The Champions Cup has served as a morale booster for Conor O’Shea’s men this season, with two wins from two belying their poor form in the Aviva Premiership.
They were on the back foot from the off though, with Leinster showing the strength of their forward pack early on and striking the first points through the boot of Ian Madigan.
Harlequins, who had their international contingent back in the starting line-up, reacted well to the early pressure, and hit back through Nick Evans’ boot, although he was taken off with an injury not long after.
Tim Swiel, his replacement, was also on target, hitting Quins into the front midway through the first half.
Both sides approached the game with the same intensity and drive, but if either side was going to cross the whitewash, it was looking all the more likely that it would the Irishmen.
They had to settle for less just before the half hour mark, with Madigan levelling through a simple penalty.
Swiel might not have expected his first European appearance to come around so soon, but he showed his composure with another penalty.
Despite a lack of tries, there was no doubt that both sides were contributing to a high quality game. With that in mind, it was probably fair that Madigan’s penalty on the stroke of half-time sent the teams in level.
The ferocious tempo of the first half was maintained after the break, with the Stoop a bundle of nervous energy. Madigan struck first with a penalty.
It was sheer force of will which saw Harlequins cross for the first try. Easter was tackled onto his back a couple of metres from the line, but threw his arms behind him whilst in full control of the ball to touch down.
That forced Leinster onto the offensive, and they paid for it just before the hour mark.
Just when the visitors looked like they would be in for a try, a pass destined for the hands of Noel Reid was intercepted by Tikoirotuma, with the Fijian running the length of field to cross the line and extend his side’s lead to nine points with 20 minutes to go.
The game was escaping the grasp of Leinster, but two penalties put them in touching distance as the final whistle neared.
Quins could have been forgiven from being nervous in the latter stages after the inconsistencies they have suffered from this season, but Danny Care showed some good game management to knock over a cheeky drop goal and keep the Irishmen at arm’s length.
That was enough for the win, although Leinster did take a losing bonus point home.
Tries: Easter, Tikoirotuma
Pens: Evans, Swiel 2
Pens: Madigan 6
Harlequins: 15 Mike Brown, 14 Marland Yarde, 13 Matt Hopper, 12 George Lowe, 11 Aseli Tikoirotuma, 10 Nick Evans, 9 Danny Care, 8 Nick Easter 7 Chris Robshaw, 6 Luke Wallace, 5 George Robson, 4 Charlie Matthews, 3 Will Collier, 2 Dave Ward, 1 Joe Marler (c).
Replacements: 16 Joe Gray, 17 Mark Lambert, 18 Kyle Sinckler, 19 Sam Twomey, 20 Jack Clifford, 21 Karl Dickson, 22 Tim Swiel, 23 Tom Casson
Leinster: 15 Rob Kearney, 14 Darragh Fanning, 13 Gordon D’Arcy, 12 Ian Madigan, 11 Luke Fitzgerald, 10 Jimmy Gopperth, 9 Eoin Reddan, 8 Jamie Heaslip (c) 7 Jordi Murphy, 6 Rhys Ruddock, 5 Mike McCarthy, 4 Devin Toner, 3 Mike Ross, 2 Sean Cronin, 1 Jack McGrath.
Replacements: 16 Bryan Byrne, 17 Michael Bent, 18 Tadhg Furlong, 19 Kane Douglas, 20 Jack Conan, 21 Isaac Boss, 22 Noel Reid, 23 Zane Kirchner
Venue: Twickenham Stoop, Twickenham