The boot of Humphreys lifted Ulster into an early 12-0 lead but Robin Copeland's score narrowed the gap before half-time.

Duncan Williams then went over at the start of the second period for what proved to be the crucial score and Humphreys failed to convert a 79th minute Nick Williams try as Munster held on for a 21-20 win.

The home side made five changes from the starting XV that comfortably beat Newport Gwent Dragons last weekend but it was the visitors who came flying out of the blocks.

With just three minutes on the clock, they earned a kickable penalty and Humphreys made no mistake with his first attempt in what would prove to be a fruitful first half for the fly-half.

Ian Keatley had a chance to almost immediately level the scores but inexplicably slid his kick wide of the uprights to leave the Ulstermen three points to the good.

And Humphreys soon doubled that lead from the tee before going three for three after 12 minutes with progressively trickier kicks.

While Keatley may have missed his first kick, the Ireland international looked a danger with ball in hand and after a scything break, only some poor handling from his team-mates cost Munster a shot at their first points.

And the boot of Humphreys made them pay once again with just over a quarter of the game gone to extend the lead to 12-0.

Keatley soon made amends for his earlier miss to cut the deficit to nine points before a beautifully worked try narrowed the gap further.

A beautiful inside pass from Duncan Williams released a marauding Ronan O'Mahony and a few phases later Copeland barrelled his way over.

However, Keatley's conversion attempt was wayward and the fly-half then cost his side a gilt-edged opportunity to score just before half-time.

A break from the lively Gerhard van den Heever left Munster with a huge overlap but Keatley put his pass behind an onrushing team-mate with the try-line beckoning to leave Ulster a 12-8 half-time lead.

But just three minutes into the second period, Williams sent the Thomond Park crowd into raptures when he picked the ball up at the base of the scrum, produced a great hand-off to repel Paul Marshall's tackle and dived over in the corner.

Keatley added the extras from close to the touchline to give the Red Army their first lead of the evening before punishing two further Ulster infringements from the kicking tee.

And on 64 minutes Munster thought they had extended their lead when JJ Hanrahan appeared to dot down after a grubber kick through.

However, the TMO ruled that he failed to cleanly ground the ball before sliding out of play.

A Keatley penalty rebounded back off the post before Stephen Archer was sin-binned for the home side and Humphreys brought Ulster within a score from the tee.

The most dramatic action was yet to come as the TMO denied Ulster a 78th minute try but they found a way over just a minute later.

Back rower Williams forced his way over from close-range off the back a ruck to make the score 21-20 before the previously perfect Humphreys slid what would have been the winning conversion narrowly wide.

There was enough time for Munster to kick-off but while trying to run the ball from deep, Ulster eventually made a mistake with 83 minutes played to bring the match to a close

It was an enthralling Thomond Park encounter and saw Munster move top of the table with previous leaders Ospreys still to play this weekend.

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