Munster overcame Harlequins 21-7 in a penalty-afflicted Heineken Champions Cup opener at Thomond Park.

Cadan Murley responded for Quins but replacement fly-half Ben Healy extended Munster's lead with a 55-metre penalty.

Flanker Gavin Coombes powered over for his first European try to seal the Irish province's Pool B win.

Quins back-row trio James Chisholm, Will Evans and Alex Dombrandt were all yellow carded along with Munster prop Stephen Archer.

In the wind and rain in Limerick, the early stages of the match were locked in midfield as defences remained firmly on top.

Hanrahan managed to break the deadlock on 13 minutes with a well-struck penalty after Quins prop Joe Marler was penalised for an off-the-ball tackle.

Mike Haley looked to have made the breakthrough when he dived over in the corner however referee Pascal Gauzere immediately pulled play back.

Marcus Smith, who was looking to implement Quins' kicking game throughout the first half, missed the visitors' first attempt off the tee and pulled another opportunity wide from 47 metres after Ireland flanker CJ Stander had been penalised for a deliberate knock-on.

Harlequins had a try disallowed after Murley went on a brilliant solo run with his pass to Ben Tapuai ruled forward before Danny Care kicked for an unmarked Dombrandt to touch down.

Hanrahan punished Quins' lack of a clinical edge when he split the posts with a 37-metre penalty before the English outfit ended the half with 14 players when Chisholm, on his 100th appearance, was carded for entering a ruck from an offside position.

Second-half spark

With the wind picking up during the interval, the hosts were reduced to 14 men seven minutes after the restart when prop Archer stopped Care from taking a quick penalty.

After a period of Harlequins pressure, momentum swung in Munster's favour when lock Tadhg Beirne thumped a clearance kick 60 metres downfield, with former England full-back Mike Brown slicing his clearance just outside the visiting 22 in response.

From the resulting line-out, Care ran into the path of Keith Earls as the Ireland wing looked to get on the end of Conor Murray's kick and Munster were awarded their first try when a maul was hauled down by Evans, who was subsequently yellow carded.

Having played an important role in the disallowed try in the first half, Murley scampered over in the corner on 56 minutes after breaking through Andrew Conway's tackle to get the visitors on the board, with Smith adding the extras.

Dombrandt was the last of the Quins' back row to be sent to the bin by Gauzere after a late hit on replacement fly-out Healy, who dusted himself down and launched a penalty between the posts from his own half.

After Smith was penalised for a tackle in the air and Healy launched a kick into the Quins 22, Coombes powered over for his seventh try in eighth matches - his first in Europe - to extend Munster's lead with nine minutes remaining.

Paul Gustard's side, who conceded 15 penalties, pressed for a late response but came up against a red wall, which held firm to maintain Munster's unbeaten start to the new season.

Munster: Haley; Conway, Farrell, De Allende, Earls; Hanrahan, Murray; Cronin, O'Byrne, Archer; Kleyn, Beirne; Coombes, O'Mahony (capt), Stander.

Replacements: Marshall, J Wycherley, Ryan, F Wycherley, O'Donoghue, Casey, Healy, Rory Scannell.

Harlequins: Brown; Earle, Lang, Tapuai, Murley; Smith, Care; Marler, Baldwin, Louw, Tizard, Young, J Chisholm, Evans, Dombrandt (capt).

Replacements: Elia, Garcia Botta, Baxter, De Carpentier, Lawday, Steele, R Chisholm.