Ronan O'Gara's injury-time drop-goal earned Munster a dramatic win over Northampton in a pulsating Heineken Cup Pool One clash at Thomond Park.
Damien Varley and Chris Ashton swapped early tries as Northampton led 13-7.
Doug Howlett's try helped Munster lead 17-13 at the break but a James Downey score then restored Saints' lead.
Vasily Artemyev wasted a chance to score another Saints try before Munster produced a last-gasp 41-phase move to set up O'Gara's winning drop-goal.
It was a thrilling finale to a remarkable match, as Northampton somehow missed out on what would have been a famous win - only Leicester have beaten Munster in Limerick in this competition.
Munster made the perfect start, with Varley on the end of a rolling maul to score in the third minute after Peter O'Mahony's kick-ahead had forced Northampton to concede a line-out deep in their own 22.
O'Gara added the conversion but Munster's lead lasted only five minutes as Northampton counter-attacked brilliantly to score a converted try, with Ben Foden's break and perfectly delayed pass setting up Ashton to score in the corner.
Ryan Lamb added the difficult conversion and his penalty then gave last year's beaten finalists the lead on 13 minutes.
As both sides looked dangerous in attack, Munster wasted a glorious chance to score a second try as Niall Ronan's forward pass prevented Conor Murray from scoring the touchdown when the home side had numbers out wide.
Northampton appeared in a degree of control when the impeccable Lamb kicked another three points in the 22nd minute after a Varley infringement.
The Saints still led by six with two minutes of the opening period remaining but Munster produced a big finish to the half with an O'Gara penalty followed by a superb Howlett try.
Northampton's defence seemed well set but the former All Blacks star completely outfoxed Foden with a jinking run and glided past another tackle to score under the posts.
Suddenly and improbably, Munster were 17-13 up at the break and the margin was quickly extended after the restart as O'Gara slotted another penalty.
But Lamb's latest penalty reduced the home team's lead to four again and the visitors were back in the lead by the 56th minute as former Munster player Downey barged his way over for a try.
There were suggestions that Lamb's pass earlier in the move had been forward but referee Nigel Owens ruled that the ball had come off O'Gara's hand.
Russian World Cup player Artemyev, who learned his rugby while at school in Dublin, wasted a glorious chance to put Northampton in firm control on 65 minutes as he knocked on with the line gaping after great work by Ashton.
Munster remained a point behind as the match entered injury time but they produced an incredible 41-phase move to set up O'Gara's drop-goal chance, which he coolly slotted from 35 metres.
It was an thrilling finish to a remarkable match and Northampton will wonder how they ended up on the losing side, although they do have the consolation of taking home a losing bonus point.
Munster coach Tony McGahan:
"It was something special. The belief in the group, the way they stuck at it for 80 minutes, a lesser side would maybe not even have been in the contest.
"Ronan O'Gara's kick at the end, he's a special person to do that, to show the bottle to put his hand up and make the kick.
"This felt like a round six encounter during the week when it actually was an opening-round game. There is a great sense of achievement for the group at this early stage."
Northampton coach Jim Mallinder:
"The mood in the dressing room is low. The feeling is one of frustration.
"I think the game hinged on some crucial refereeing decisions - I felt the referee got quite a lot wrong.
"Sometimes you don't always get the rub of the green and I think we will look back and probably say we did not quite get it."
Munster: Murphy; Howlett, Barnes, Mafi, D Hurley; O'Gara, Murray; Du Preez, Varley, Botha, D Ryan, O'Connell, O'Mahony, Ronan, Coughlan.
Replacements: Chambers for Barnes (66), O'Leary for Murray (61), Hayes for Botha (70), D O'Callaghan for D Ryan (54).
Not Used: Fogarty, J Ryan, Leamy, Keatley.
Northampton: Foden; Ashton, Clarke, Downey, Artemyev; Lamb, Dickson; Tonga'uiha, Hartley, Mujati, Lawes, Sorenson, Clark, Wood, Wilson.
Replacements: Roberts for Dickson (66), A Waller for Tonga'uiha (69), Dowson for Clark (66).
Not Used: Haywood, Doran-Jones, Manoa, Myler, Pisi.
Referee: Nigel Owens (Wales)