Paris - Coach Mark McCall made nine changes as Saracens' hopes of defending their European Champions Cup title were dealt a blow with a 10-3 defeat at Munster on Saturday.
The English champions, who have been fined and deducted points in the Premiership for salary cap irregularities, rested England's Owen Farrell as well as Billy and Mako Vunipola for the bonus point loss.
It leaves them third in the Pool 4 standings, five points behind the Irish province and six behind Racing 92.
McCall said he is planning to recall some of his front-line players as they host two-time winners Munster next Saturday.
"Some of the people who haven't played today will play," McCall said.
"Some of our non-internationals who have had a really busy eight weeks or so, they'll get some rest," he added.
In the other game in the group, Racing hammered 14-man Ospreys 40-19 to remain top thanks to a bonus point for scoring four or more tries.
On the Irish west coast, the only points of a tense opening quarter came from a JJ Hanrahan penalty on 18 minutes.
The hosts thought they had stretched their advantage four minutes later but Chris Farrell's try was ruled out by the video referee.
Captain Peter O'Mahony scored the only try of proceedings on the half hour mark, crashing over from short-range as Hanrahan slotted the easy conversion.
Ben Spencer kicked a late penalty and the Irish side led 10-3 at the break.
Scrum-half Spencer wasted a chance to close the gap to four points, missing a 44th minute penalty as the wind inside a packed Thomond Park pushed his effort wide.
In a sluggish final 30 minutes, the home side held on as any attempts to play attractive were hampered by the damp conditions.
Earlier Ireland flyhalf Johnny Sexton suffered a knee injury as four-time winners Leinster hammered in-form Northampton 43-16.
Sexton, 34, who has 94 Test appearances to his name, hobbled off the field at Franklin's Gardens on the 44-minute mark after a collision in a tackle.
"He's a little uncomfortable there at the moment," said head coach Leo Cullen.
"I don't know the extent of it, but we'll find out more in the early part of next week."
Seven different players crossed for the Irish province who move five points clear at the top of Pool 1 thanks to the bonus point victory.
Elsewhere in the group, French league leaders Lyon claimed their first ever success in the top-tier competition beating Italians Treviso 28-0.
In Pool 3, uncapped Irish scrum-half John Cooney slotted a 78th minute penalty to clinch a 25-24 win over Harlequins to move Ulster back to the top of the table after Clermont had beaten Bath 34-17 on Friday.
Despite trailing by 12 points after 38 minutes, Glasgow beat La Rochelle 27-24 thanks to Kyle Steyn's 64th minute try which lifted the Scottish outfit to second in Pool 2 before unbeaten Exeter Chiefs host fellow English side Sale Sharks on Sunday.
In Pool 5, South Africa's Rugby World Cup winner Cheslin Kolbe is set for a return with Toulouse as the Top 14 champions host Montpellier and Gloucester welcome Connacht.