Springbok centre Jean de Villiers made his debut for Munster as Williams' first Magners League tries inspired the defending champions to a bonus point victory over the Dragons.

Number eight Williams, who endured an injury-interrupted first season with Munster, had his best game in red, with fellow New Zealander Doug Howlett also touching down.

The Dragons tired in the second half and James Arlidge's penalty just before half-time proved to be their only score.

A stomach bug prevented returning Lion Keith Earls from taking his place at full-back, meaning positional switches for Felix Jones and Barry Murphy and a late promotion from the Munster bench for newcomer de Villiers.

Lions duo Ronan O'Gara and Donncha O'Callaghan also made their first starts of the season.

Beaten heavily on their last two visits to Cork, the Dragons made three changes to the side that scored a bonus point win over Glasgow last weekend, full-back Martyn Thomas, prop Hugh Gustafson and flanker James Harris earning recalls.

Munster started well, de Villiers winning a penalty on halfway and then setting up his centre partner Lifeimi Mafi for a jinking run into the 22.

The Dragons gradually gained territory and turned down a kick at goal before Munster, with a strong defensive scrum, were able to force a turnover and clear the danger.

Jones, Mafi and Denis Hurley saw plenty of possession in the first quarter but Munster grew frustrated by the Dragons' well-organised, aggressive defence and O'Gara had to react sharply to prevent Ashley Smith from releasing a team-mate for the line.

O'Gara missed his first shot at the posts but the deadlock was finally broken five minutes before half-time when he split the posts after a scrum infringement by Nigel Hall.

Arlidge quickly replied with a penalty of his own and was narrowly wide with an injury-time drop goal attempt following a terrific midfield break by Joe Bearman.

Despite these signs of promise, the Dragons lost their way in the second half as Tony McGahan's men upped the intensity.

Five minutes in, Williams crashed over off the base of an advancing five-metre scrum to register Munster's first try.

Although they were hampered by injuries to Murphy and Alan Quinlan, Munster pressed on and pinned the visitors back in their own half for much of the remainder.

O'Gara and Dragons replacement Shaun Connor were sent to the sin-bin for a bout of fisticuffs at a ruck close to the Welsh side's line and just moments later, Williams used his brute strength to barge past Harris and Martyn Thomas for his second touchdown.

Scrum-half Tomas O'Leary added the conversion and did likewise after replacement Howlett speared through a gap and outpaced Aled Brew to score behind the posts.

The Dragons tried valiantly to mount a comeback but Munster sewed up the bonus point, eight minutes from the end, when Williams took a quick tap and bulldozed his way over again from close range.

Munster's third successive win over Welsh opposition saw them vault up to second place in the league table, level on 13 points with their fiercest rivals Leinster whom they meet in next Saturday's clash of the champions at the RDS.