tHE old sporting adage about a game of of two halves barely does this match justice.

Ireland fully deserved to take a huge first step towards contention for the 2013 RBS 6 Nations championship by winning a rip-roaring battle in Cardiff, but had to withstand immense second-half pressure before doing so.

Trailing by 27 points only two minutes into second half – a deficit never overcome in the 142-year history of international rugby – Wales attacked almost continuously. Ireland defended desperately, and at times illegally – hooker Rory Best and scrum-half Conor Murray both going to the sin-bin – but it was not until the final few minutes that they could be confident that their massive lead was sufficient insurance.

Had Wales done the improbable, it would have been tough to see past replacement flanker Justin Tipuric as the hero of the hour. Wales were transformed from the moment he replaced Aaron Shingler after Ireland's third try had taken them into a 30-3 lead in the 43rd minute.

Instead the plaudits rightly fell to the scorer of that try, Brian O'Driscoll. The 34-year-old centre turned his first match since losing the captaincy to Jamie Heaslip into a showcase for what has made him great. Ireland's first try was scored by wing Simon Zebo, but was an O'Driscoll creation – the player thrusting between two defenders to a point where he could have scored himself, but instead chose to give Zebo an elementary touchdown.

The post-interval score, extending O'Driscoll's all-time Six Nations try-scoring record to 26, was drawn from his mid-period, driving over from close range after Rob Kearney had been brought down a yard short.

And the final stages saw him take on the demanding role of scrum-half when Murray was sin-binned with 10 minutes to go, and carrying it off with some aplomb. "He was the difference between the two teams. I wish somebody had left him in Ireland," said Wales's defence coach Shaun Edwards after the match.

In between the two O'Driscoll-created scores came one from a Welsh error. Dan Biggar's clearance was charged down by Best, Zebo performed some extraordinary sleight of foot to control an ill-directed pass from Jamie Heaslip and prop Cian Healy drove over from close range.

The charge-down epitomised a period during which the reigning Six Nations champions degenerated into a hapless rabble, with Ireland dominating every phase of play.

As interim head coach Robert Howley said : "You need a foothold in the game, whoever you are playing. We didn't give ourselves a chance."

Outside-half Jamie Sexton made sure Ireland capitalised fully, kicking with precision from the hand and landing every chance at goal he was offered – three conversions and three penalties.

At 30-3, an Irish half-century looked entirely possible. It was to Wales' credit that they hit back. Ireland captain Jamie Heaslip said: "It seemed like wave after wave of attack" and added he had "walked off the field with nothing in the tank".

Tries by wing Alec Cuthbert and full-back Leigh Halfpenny had Wales back to 30-15 with the final quarter still to come. But Ireland hung on for another 16 minutes until prop Craig Mitchell crashed over for his first international try only three minutes after replacing Adam Jones. However, the challenge of scoring twice in the final four minutes was always too much of an ask.

"Some of the defence in the second half, you simply can't coach", said Ireland coach Declan Kidney, whose team now face England in Dublin next week with the momentum and confidence that come with a first win away. Wales must go to Paris, where they last won in 2005.