Munster just hung on in a tense Thomond Park finish for a one-point victory against Ulster tonight, winning 21-20 to move top of the Guinness PRO12 table.

Ulster opened the scoring with an Ian Humphreys penalty after three minutes and they were clearly the stronger side in the initial 20-minute period with indiscipline proving a worry for Munster.

Three further successful penalty kicks from the Ulster out-half gave the visitors a deserved 12-nil lead before Ian Keatley kicked Munster's first points after 23 minutes.

On making his first start for the province Pat Howard was an early replacement five minutes later after a collision with fullback JJ Hanrahan, and Andrew Smith was introduced to the back-line.

Munster reduced the margin further with a try from man-of-the-match Robin Copeland after 29 minutes.

It was Duncan Williams and Ronan O'Mahony that instigated the attack with the scrumhalf sending a reverse pass to the flying winger who swerved around the Ulster defence before being stopped short of the five metre line. Williams was at the breakdown quickly and released the ball wide with Keatley and Hurley playing their part before Copeland ran over for the first try of the game.

Keatley missed the conversion and it remained 8-12 until the break despite a clear-cut scoring opportunity minutes later.

Powerful winger Gerhard van den Heever broke through the Ulster defence and when the ball was flashed wide with a numbers advantage Keatley was unable to find his target and Botha or Stander missed out on a certain try before the break.

In the second half Duncan Williams put Munster ahead for the first time three minutes in after he took a solo run off the back of a poorly controlled Munster scrum. He held off his opposite number Paul Marshall and dived over in the corner for Munster's second try. Keatley added the difficult touchline conversion to put Munster ahead by three.

Two successive penalties from Keatley increased the tally and with 21 unanswered points the attacking momentum continued with van den Heever again causing trouble for the Ulster men's defence. He linked well with Keatley to bring play into the opposition 22 before JJ Hanrahan stretched for a possible third try. A Stuart Olding tackle and TMO decision denied the advantage.

Ulster fought back when Munster were reduced to 14 men after Stephen Archer was binned for taking the support player out in the lineout. The Northerners turn of momentum led to a dramatic finish when Humphreys added his side's fifth penalty and they moved within six points with 8 minutes remaining.

Making use of the numerical advantage Neil Doak's men continued to attack with their lineout and maul proving effective and Nick Williams crashed over for the visitors try on the 79th minute.

Munster thought it was all over but the men in red escaped defeat when Humphreys missed his first shot at goal with the conversion and Anthony Foley's charges held on to claim a one-point victory.

Munster: JJ Hanrahan (Felix Jones 66), Gerhard van den Heever, Pat Howard (Andrew Smith 28), Denis Hurley, Ronan O'Mahony; Ian Keatley, Duncan Williams; John Ryan (Dave Kilcoyne 49), Duncan Casey, BJ Botha (Stephen Archer 67); Donncha O'Callaghan – capt, Billy Holland; Robin Copeland (Tommy O’Donnell 49), Paddy Butler (Paddy Butler 77), CJ Stander.

Replacements: Kevin O'Byrne, Dave Kilcoyne, Stephen Archer, Tommy O'Donnell, Sean Dougall, Neil Cronin, Andrew Smith, Felix Jones