World Cup Super 8, Barbados:
Australia 92-1 (12.2 ovs) bt Ireland 91 (30 ovs) by 9 wkts
O'Brien was beaten for pace by the unpredictable Tait
Australia needed less than 13 overs to seal a semi-final place, after bowling out Ireland for 91 in Barbados.
Glenn McGrath struck in the first over and after the rapid Shaun Tait took two wickets in two balls, it was soon 12-4.
At that stage Ireland were in danger of the lowest World Cup total, 36 made by Canada in 2003, but John Mooney's defiant 23 helped bolster their score.
In reply, Adam Gilchrist hit a rapid 34 and Mike Hussey (30) secured a nine-wicket success with a six.
There were immediate concerns for the longevity of the contest when Ricky Ponting announced Australia would field, scuppering suggestions he wanted to give some batsmen extra practice.
Glenn McGrath needed only six deliveries to increase his lead at the top of the World Cup wicket-takers.
The gap between Jeremy Bray's bat and pad was as wide as the Liffey as the left-hander departed for a single.
Tait was soon in excess of 90mph, and his second over was full of incident.
Having beaten William Porterfield for pace with one that was marginally he shattered Niall O'Brien's stumps when the left-hander was also late on his shot and got an inside edge.
The hat-trick ball whistled past Kevin O'Brien's outside edge at 92mph and the burly all-rounder then tried his utmost not to show his pain when he ducked into a brutal bouncer that thudded into his shoulder.
O'Brien regained his composure to clip the final two balls of the over off his toes to the boundary and give the many exuberant Irish supporters something of a cricketing nature to cheer.
Although the wickets dried up - for six overs in any case - the punishment did not relent for the batsmen.
Andrew White received a sickening blow to the side of the visor from McGrath, who soon afterwards defeated him with a slower ball in an opening six-over spell in which he took 3-9.
Gilchrist played his customary array of fluent, attacking strokes
Extras was becoming an important contributor to Ireland's cause, and Tait showed the erratic side of his game with four wides and a no-ball in an over.
The 50 was recorded in the 15th over with the eighth wide of the innings and although wickets continued to fall, Trent Johnston and then Mooney valiantly inched their side towards the elusive three figures.
Mooney, sporting a Mexican bandit-style moustache, shared the longest partnership of the innings, a 41-ball stay of execution with gangly last man Boyd Rankin.
But having survived two run-out scares when the fielders failed to hit the target, the battling left-hander was short of his ground attempting to keep the strike when Tait threw down the stumps from mid-off.
Australia began their innings with an hour to play before the lunch interval scheduled to take place between innings.
Hussey was sent in to open with Gilchrist to get some practice in the middle, having made four single figure scores in the tournament and not being required in the last two matches.
There was a danger Gilchrist was going to score the bulk of the runs before Hussey as the wicket-keeper launched into Dave Langford-Smith and had 24 to his name after five overs.
He was dismissed by a good one from skipper Johnston, who nipped one back off the seam and was able to perform his unique celebratory dance.
The only remaining question was whether the Australians could complete victory before the interval.
Andrew Symonds, moved up to number three, gave them an excellent chance of doing so with a brutal flat-batted straight six.
With five minutes remaining 10 were still needed, but Hussey lofted Kyle McCallan into the leg-side for four.
The small children in the crowd were screaming for a six, and Hussey obliged by hooking Rankin into the crowd at mid-wicket to wrap things up in the final over before the break.