Howlett (right) soothed Munster nerves when he scored his second try late on
By James Standley
Munster clinched a Heineken Cup semi-final against Biarritz as they fought back from a half-time deficit to finally subdue Northampton.
The hosts took an 8-0 lead via a Ronan O'Gara penalty and Paul Warwick try.
Stephen Myler then landed two penalties and although Doug Howlett went over, a Myler penalty and converted Jon Clarke try gave Saints a 16-13 half-time lead.
But Jean De Villiers's try put Munster back in front and O'Gara's boot and a second Howlett try saw the Irish home.
After two classics in the weekend's first two quarter-finals a rocking Thomond Park was the ideal stage for another pulsating encounter, and the two sides did not disappoint as they served up a hugely entertaining match.
The two teams had met in the pool stages and although Munster topped the group, in their head-to-head matches each side won a game apiece - Northampton triumphing 31-27 at Franklin's Gardens and Munster winning the return 12-9.
The hosts suffered a blow before kick-off, with captain Paul O'Connell forced out with a groin injury, but they shrugged off his absence to boss the opening stages and went in front inside the first two minutes as Ireland fly-half O'Gara knocked over a penalty.
Their first try soon followed. A forward rumble put Saints on the back foot and when Munster went wide, Keith Earls drifted outside Clarke before feeding Warwick, who dummied his way over with a man spare outside.
O'Gara missed the conversion and any thoughts the passionate home fans, who were the vast majority in the capacity 26,000 crowd, may have had of an easy afternoon's work were rapidly dismissed as Northampton fought back with vigour and notched two quick penalties from Myler.
First Alan Quinlan was penalised for being a lazy runner as Saints scrum-half Lee Dickson looked to move the ball from the base of a ruck, before the Northampton front row marched mercilessly forward to win a penalty at a scrum.
No pack likes being driven backwards, especially not in front of their adoring fans, and when the Munster eight were given the chance of redemption five minutes later they took it in style, turning the tables on Saints at a scrum to secure possession.
O'Gara then broke blind and fired a wide pass to Howlett, and the former All Black winger forced his way over despite a despairing tackle from fellow New Zealander Bruce Reihana.
O'Gara could not convert and although they had enjoyed the upper hand for the majority of the half, Munster were to go in trailing at the break.
Myler trimmed the gap to four points with a penalty when Quinlan again infringed and seconds before the break the visitors went in front with a superb try.
Northampton switched the ball from left to right and when they came back the other way crisp passing enabled Ben Foden to draw the last defender and send Clarke over.
Warwick's early try set Munster on their way to the last four
Myler converted to make it 16-13 but Munster are not two-time champions for nothing and they went back in front with a try of mathematic precision from De Villiers after 53 minutes.
Tomas O'Leary broke across field from the base of a five-metre scrum and De Villiers appeared on a precise 90 degree angle to burst between Myler and James Downey.
O'Gara converted and although Myler cut the gap to a point with his fourth penalty, O'Gara soon replied in kind before unveiling some pin-point kicking from hand to keep Northampton pinned in their half.
The Saints brought on the greater running threat of Shane Geraghty at fly-half in place of Myler in an attempt to outflank the hosts, but having re-established their lead they were in no mood to relinquish it.
Northampton did manage to cause some alarm as Juandre Kruger was hauled down in the corner after crisp interplay between Geraghty and Ashton.
But Munster marched back upfield and wrapped up victory when Howlett crossed out wide with five minutes remaining.
O'Gara drilled the conversion through the middle to leave the home fans plotting the best way to San Sebastian and a semi-final against Basque aristocrats Biarritz.
Northampton boss Jim Mallinder:
"We talked at half-time about what O'Gara would do, though unfortunately talking isn't quite good enough and he's a master.
"It was quite windy out there and he controlled that second half particularly well. O'Gara's a good player and Munster are a good team.
"We couldn't really get out of our half in the second half. We thought we could break Munster down by playing some rugby and if we looked after the ball we could score some tries, but we needed quality ball but didn't get enough of that.
"We knew we had a chance of winning this game, a good chance. We just didn't perform the way we know we can, but the best team won on the day."
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