Two-time European Cup champions Munster ensured they host one of the quarter-finals on Friday when they edged out Pool One rivals Northampton 12-9 to reach the last eight for a remarkable 12th time in a row.
Ireland fly-half Ronan O'Gara kicked all their points while Saints will at least take away a defensive bonus point which puts them in a good position to make the quarter-finals as one of the two best runners-up depending on the weekend's other results.
"Northampton are a tough team and were on a run of 10 successive victories," said Munster captain Paul O'Connell.
"We are very happy to win, we didn't play fabulous but we dug deep, especially when I was sin-binned."
Northampton's director of rugby Jim Mallinder was proud how his mainly young side had performed against the battle-hardened opposition.
"We made some wrong decisions out there but I thought we had the upper hand in the second-half," said Mallinder, who will have been concerned by the sight of Christian Day being stretchered off at the final whistle.
"We've done all we can, we more than matched them but we just didn't take our opportunities."
Munster took the lead in the third minute through O'Gara calmly slotting over a penalty.
Munster's veteran flanker and man of the match Alan Quinlan - who will be 36 later this year - and Saints flying winger and former rugby league star Chris Ashton were having a great old tussle with the older man coming off the worse when Ashton clipped him.
O'Gara had the chance to extend the lead shortly before the half hour mark but his penalty from just inside Northampton's half fell short - former All Black Bruce Reihana, though, made no mistake for the visitors from 48 metres out and levelled the match in the 31st minute.
However, a fine incisive run by O'Gara brought another penalty to the hosts after a Northampton player dove in too early to break down the attack just metres from the line - O'Gara had no problem in converting the penalty to give Munster a 6-3 lead at the break.
Shane Geraghty - who was having a curates egg of a match - levelled in the 54th minute with a penalty, redeeming himself after making a terrible hash of a previous effort.
O'Gara restored Munster's lead in the 57th minute with a penalty from in front of the posts, though, O'Connell was testing referee Roman Pointe's patience with a series of verbal exchanges. The Frenchman made it clear who was in charge with a retort of 'we do it my way'.
However, Pointe's and O'Connell's titanic struggle mirroring that of the two teams saw the British and Irish Lions captain yellow carded on the hour mark for hands in the ruck.
"I was steaming angry about being sin-binned," said O'Connell.
"A lot of things were confusing out there. However, thats what what happens when one has no communication and its just dictation."
Despite Northampton, though, twice opting to take a five metre scrum, with O'Connell off, instead of kicking for goal it was heroic scrummaging by the hosts that saw them win one against the head and clear the danger.
Incredibly it was the Irish province that scored with O'Gara adding another penalty when Ashton was penalised and if the roar for the score was deafening it was outdone in volume by the return of the talismanic O'Connell.
Geraghty went off to be replaced by another rugby league convert in Stephen Myler, who made the last five minutes a nervy one for the hosts as he landed a penalty to make it 12-9 - and whilst they may not have won, the bonus point could prove to be as good as a victory.
Copyright 2010 AFP Global Edition
