It was less good news for O'Connell's Ireland teammate Brian O'Driscoll who has now played the last European game of his career after Leinster lost to defending champions Toulon.
And Ulster battled valiantly despite being down to 14-men for almost the entirety of their quarter-final after Jared Payne's early red card, but the Irish region could not quite hold off Saracens.
There were also two re-arranged clashes in the RaboDirect PRO12 as Edinburgh staved off a late assault at Rodney Parade to record their first away league win of the season with a 23-19 victory over Newport Gwent Dragons.
And two tries from Henry Pyrgos and a stunning performance from Sean Maitland saw Glasgow Warriors storm back into the play-off places with a 29-10 victory over Benetton Treviso.
TRY OF THE WEEKEND
It was fitting that after a totemic performance in the second-row, the Munster marvel that is Paul O'Connell went over for the Irish region's final try of the game, crashing over for the Red Army's sixth score under the posts to heap more misery on Toulouse.
BREAK OF THE WEEKEND
Hosea Gear's score for Toulouse had threatened a French fightback at Thomond but Casey Laulala had other ideas.
Quick turnover ball released the former All Black centre into space down the left and despite having numbers in support, Laulala had too much pace on his own for the covering Toulouse defence and raced clear to touch down.
PLAY OF THE WEEKEND
Sean Maitland made his return from injury, making his first start since December for Glasgow against Treviso.
And the Kiwi-born utility back did not disappoint with two storming breaks down the right wing that laid on two tries for his scrum-half Henry Pyrgos.
PLAYER OF THE WEEKEND
The return of Peter O'Mahony to the Munster starting line-up barely lasted a quarter of an hour but the Irish region didn't exactly miss their skipper, such was CJ Stander's superb performance off the bench.
The back-rower scored a crucial try soon after half-time to stretch Munster's lead over four-times European champions Toulouse.
But that score barely scratched the surface of Stander's superb all-round performance that saw him take home the man-of-the-match award.
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