Connacht (9) 19
Try: McCarthy Cons: Keatley Pens: Keatley 4
Leinster (9) 18
Pens: Contepomi 6
Robbie Morris celebrates Connacht's win in Galway
Connacht claimed a shock Magners League win over defending champions Leinster in Sunday's clash in Galway.
Ian Keatley came back to haunt his old province as he kicked four penalties and converted Mike McCarthy's lone try.
McCarthy was sent off immediately after his 44th-minute score following a clash with Rocky Elsom.
The sides were level at 9-9 at the break but Leinster's points all came from Felipe Contepomi penalties as Connacht produced remarkable defending.
Michael Bradley's men required a real backs-to-the-wall effort to hold on to their lead.
After weathering a storm in which Leinster fluffed numerous try-scoring chances, the hosts' seven-man pack wound down the clock with a superb spell of possession rugby.
Wanting to bounce back from last week's reversal to Munster, Leinster threatened twice in the opening five minutes through Rob Kearney and Luke Fitzgerald.
Felipe Contepomi, making his 100th appearance for the visitors, did boot his side into a 9-3 lead with Connacht second row McCarthy having already been rather harshly sin-binned for bringing down a lineout.
But Connacht, with Johnny O'Connor impressing in front of the watching Ireland head coach Declan Kidney, battled back to 9-9, while still down a man, with Keatley slotting two penalties.
Connacht scrum-half Frank Murphy (right) tackles Sean O'Brien
Five minutes into the second half, the westerners conjured up a bit of magic for only their third try of the campaign.
O'Connor tore out of his half to begin the move and Frank Murphy, Keatley and hooker Sean Cronin were all involved before McCarthy charged under the posts.
A dust-up ensued after the try and McCarthy was spotted leading with his head on Rocky Elsom and the Australian retaliated with a punch.
Both players received yellow cards, meaning the try-scorer's night was over.
Keatley converted and crucially managed to trade penalties with Contepomi while both sides were down to 14 men.
Leinster shunned an immediate shot at the posts as, with Elsom back, they pressed for a pushover try but Connacht somehow held out.
Contepomi did land a further brace of penalties but Luke Fitzgerald, Elsom and Cian Healy all failed to convert glorious try-scoring chances while Jonathan Sexton pushed a drop goal shot inches wide.
Connacht held possession splendidly in the closing minutes to earn their first victory over an Irish province since December 2005 and move off the foot of the table in the process.
The defeat was the last thing Leinster coach Michael Cheika needed ahead of Saturday's Heineken Cup opener in Edinburgh.
Connacht: Carr, Bibo, Duffy, Deane, Roberts, Keatley, Murphy, Wilkinson, Cronin, Loughney, McCarthy, Farley, J Muldoon, O'Connor, Rigney. Replacements: Hearty for Roberts (67), Nathan for Keatley (72), C Muldoon for Cronin (67), Morris for Loughney (50), Swift for Rigney (63).
Not Used: Browne, Campbell.
Leinster: Kearney, Horgan, Fitzgerald, Contepomi, S. Keogh, Sexton, Keane, Wright, Fogarty, van der Linde, Cullen, Toner, Elsom, O'Brien, S. Keogh. Replacements: Healy for Wright (47), Hogan for Toner (64), Jowitt for O'Brien (42).
Not Used: Blaney, McFadden, Jones, Brown.
Referee: George Clancy (IRFU).