In wet and windy conditions, Ireland opened their pool campaign with a hard-earned victory over the USA, which puts them a point behind Australia ahead of the sides' crunch clash in Auckland next Saturday.

A try from Rugby World Cup debutant Tommy Bowe on the cusp of half-time saw Declan Kidney's men move 10-0 ahead and further tries from Rory Best and Bowe settled the issue.

Although the performance was patchy and the error count high, Ireland dominated the set piece area and defended solidly until gifting Paul Emerick a late intercept try.

Brian O'Driscoll admitted afterwards that they 'have a lot to improve on' as they approach a six-day turnaround leading into the game against the Wallabies, who beat Italy 32-6 in their opener.

Jonathan Sexton had an off night with the boot at Stadium Taranaki, missing his first shot at the posts after the Irish pack gobbled up the ground at a scrum.

A slashing break through the middle by Keith Earls could have led to the first try-scoring chance, but the winger could not link with Jamie Heaslip, who ran a good support line.

The USA managed to bring down Paul O'Connell in front of their posts as Ireland stayed on the front foot, however it remained scoreless with Sexton's 12th-minute penalty attempt drifting to the right and wide.

The large Irish contingent in the crowd made their presence felt with chants of 'Ole, Ole' and a blast of 'The Fields of Athenry'. A half break from Conor Murray, on his full debut for Ireland, gave his half-back partner the chance to make amends and Sexton duly delivered to make it 3-0.

But unforced errors started to creep into Ireland's game, allowing the Americans to build some passages of play. Their Christchurch-based winger James Paterson missed a penalty kick from the left after Best was caught offside.

Into the rain-hit second quarter, Emerick and new record caps holder Mike MacDonald got on the ball as scrum half Mike Petri gleaned quicker ball at ruck time.

Eddie O'Sullivan's men crowded the midfield in an attempt to thwart the influence of O'Driscoll and Gordon D'Arcy, but the latter almost put Bowe through on the right as Ireland got back on the attack.

A strong carry from Stephen Ferris, one of Ireland's best performers, got the men in green in scoring range again, only for Earls to be called back for an earlier infringement after he had stretched over the try-line.

The game was stop-start in nature and needed a try to spark it into life. The conditions did not help Bowe as he tried to gather Sexton's cross-field kick, and a Ferris surge was spoilt by a subsequent knock on from Murray.

But Ireland drove the Americans backwards at the next scrum and Sexton used the turnover to raid up the left. The impetus was there and with seconds left in the first half, Bowe took a short pass from Sexton, beat the initial tackle and glided over by the posts.

Sexton converted for a 10-0 half-time lead, the enhanced margin rewarding the likes of Shane Jennings, Best and O'Connell for their efforts at successive rucks before Bowe made the breakthrough.

Sexton drew a couple of penalties to the left of the target, as the second half got underway. The Americans' all-action skipper Todd Clever was a galvanising force for them, particularly in defence, and they continued to make their tackles and hit rucks hard.

A positive run from Blaine Scully and a series of rucks in the Irish 22 set up Paterson for a well-struck penalty goal which punished Donncha O'Callaghan for not rolling away.

Soon after though in the 56th minute, Ireland conjured up their second try. A sliced American clearance allowed them thunder forward from a lineout maul. Hooker Best broke away and slipped out of last-ditch tackles from Clever and Takudzwa Ngwenya to score in the left corner.

Ronan O'Gara, who came on in a double switch at half-back, missed a difficult conversion. The lead was extended to 22-3 on the hour mark, Bowe and Brian O'Driscoll profiting from quick ruck ball and some precise passing as the Monaghan man crashed over for his second try.

O'Gara had the measure of the conversion kick this time and changes were made up front and out wide by the Irish management.

Jerry Flannery and World Cup debutant Tony Buckley were added to the front row, Denis Leamy came on in the back row and Andrew Trimble's introduction for Murphy saw Earls move to full-back.

Ireland's drive for a bonus point score ended in disappointment though, amid some poorly-constructed attacks and a general lack of verve.

The Eagles continued to tackle with gusto - witness Nic Johnson's thumping hit on Eoin Reddan and their defiant scramble to defend a late maul and series of scrums.

O'Connell, a deserved man-of-the-match winner, claimed a lineout in the American 22 as Ireland continued their hunt for try number four. O'Gara opted for a dink over the top and Earls was just beaten to the bouncing ball by replacement Tim Usasz.

Time was almost up but the concession of a last minute try added to Ireland's sense of frustration. D'Arcy's loose pass in midfield was intercepted by Emerick who raced in under the posts from 50 metres out. Replacement Nese Malifa converted with the final kick.