All of Leinster's points came from the boot of Felipe Contepomi (right)
Leinster coach Michael Cheika admits his side must raise their game another notch if they are to beat Heineken Cup favourites Munster in the semi-finals.
Leinster squeezed past Harlequins 6-5 on Sunday, a week after losing 22-5 to rivals Munster in the Magners League.
"We understand the challenge we will be coming up against and we have to improve on that again," Cheika said.
"It's always a very tough match when we come up against our southern rivals. We know what is at stake."
Leinster's victory at The Stoop sets up a repeat of the 2006 Heineken Cup semi-final, which Munster convincingly won 30-6 on the way to their first European crown.
That was one of three semi-final defeats in the competition for Leinster, all at Lansdowne Road. They were beaten 23-14 by Cardiff in the inaugural competition in 1996, and 21-14 by Perpignan in 2003.
This year's semi-final will take place at Dublin's Croke Park on 2 May, with a 1730 BST kick-off.
"A lot of the players are used to playing there," noted Leinster captain Leo Cullen, whose side includes Rob Kearney, Brian O'Driscoll, Gordon D'Arcy, Luke Fitzgerald and Jamie Heaslip, while Munster boast 11 members of Ireland's Grand Slam-winning squad.
"We played them [Munster] last week and they beat us convincingly on the scoreboard," Cullen added. "It's going to be tough but we do not expect anything less in a Heineken Cup semi-final."
Six points from the boot of Argentine international Felipe Contepomi were sufficient to propel Leinster into the last four, although they were forced to defend for large parts of the second half camped on their own tryline.
"We made too many mistakes in the first half and in the second we just had to defend," Cheika added.
We're out of one competition but we're still in another
"But we showed a lot of character, and that is important. It can get you through those sort of games when you are not at your best.
"We pride ourselves on our approach to defence, but we need to build it up to another level (for Munster)."
Harlequins were left to rue a missed penalty apiece from Nick Evans and Mike Brown, along with a wide conversion attempt from replacement Chris Malone.
"Those eight points were probably the difference between the sides," said Quins director of rugby Dean Richards.
"Small things make big differences and we missed those kicks, but the boys tried extremely hard and put a huge effort in.
"We're out of one competition but we're still in another [the Guinness Premiership], so let's look forward."