London - Munster made the most of a yellow card given to Saracens prop Rhys Gill as they defeated last season's losing finalists 14-3 in a European Rugby Champions Pool One clash at Thomond Park on Friday.
But one consolation for Sarries was that outside-half Owen Farrell made his first start for five weeks following a thigh strain and played a full 80 minutes, a fortnight before England face world champions New Zealand at Twickenham.
As rain fell steadily, a tight first half ended all square at 3-3 after Ian Keatley and Farrell kicked a penalty apiece.
But with Gill in the sin-bin for a tip tackle on CJ Stander, a driving Munster maul led to replacement forward David Kilcoyne scoring the only try of the match on the hour mark.
Keatley, who landed just two out of six shots at goal, added a drop-goal to seal a victory that took two-time European champions Munster, narrow 27-26 winners in their tournament opener against Sale last week, to the top of Pool One.
"We are in a good position, but that is all it is," said Munster coach Anthony Foley.
"We have eight points. We have Clermont back-to-back in a few weeks' time, but we have a lot of work to do between now and then."
Saracens director of rugby Mark McCall, while disappointed not to take a losing bonus point from the game, said there was still all to play for.
"I think the pool is wide open," he said. "We would have, as a minimum, wanted to take five points from our first two games. You have the win the first one and come away with a losing bonus from the second.
"The fact we scored four tries and got a bonus last weekend against Clermont was a big bonus," the former Ireland international added.
Saracens pressed hard at the start of the second half, with England discard Chris Ashton looking especially lively on the wing and they looked the more likely of the two sides to score a try until Gil's indiscipline cost the London club dear.
Keatley's second successful penalty edged Munster 6-3 in front.
There was a potentially controversial moment when, extraordinarily, the television match official denied Munster wing Andrew Cowie what seemed a perfectly good try in the corner.
Fortunately for Munster and their typically passionate fans, it was not a decisive turning point in the match.
Munster soon had a close range line-out and from the ensuing catch and drive Kilcoyne, only on the field for a matter of seconds, was at the tail end of a maul that Saracens were powerless to resist as the Irish province scored the game's lone try.
"For us to take that blow and then go straight back down and score directly off that line-out says something about the character which is in the team," Foley said.
Keatley could not convert and Saracens were still in the match before he put the result beyond doubt with a drop-goal from in front of the posts.