ALTHOUGH the wind was blowing in off the Southern Ocean there were few cool heads to be seen in the closing overs of the game in Hobart yesterday.

Brainless bowling, sloppy fielding, a controversial catch and panic-stricken batting abounded as the margins between Ireland and Zimbabwe narrowed. But Alex Cusack is blessed with the coolest brain and nerve in Irish cricket and he had the ball in his hand.

Just moments before, an ashen-faced Kevin O'Brien's final over had yielded 19 runs, leaving the Africans to score just seven off the last six balls, with two wickets in hand. It was a cruel contrast with the last time O'Brien bowled the 49th over in a World Cup game with Zimbabwe - in 2007 he sent down a maiden to help force a tie.

Cusack rambled back to his mark and ran in to Regis Chakabva. He bowled a slower ball - his speciality - and the batsman's swipe could only drag the ball onto his stumps. Next ball squirted away for one, leaving Cusack to take on Tamara Mupariwa, who had taken O'Brien apart the over before. Another slower ball foxed him and he lofted it high to William Porterfield, the safest hands on the team.

Zimbabwe were livid afterwards, believing John Mooney's foot had brushed the rope when catching Seán Williams at a vital stage. "You've got to take his word for it", said captain Brendan Taylor. "They zoomed in, and I thought it was pretty clear. But you've got to take the fielder's word."

While initially the boundary seemed to move, repeated viewing suggests the shadows cast by Mooney's leg gave that impression. The fielder checked where his foot was before starting his celebrations - like Roger Hunt's reaction in 1966, the sportsman's delight at success is hard to fake. "It's very hard to tell when you're on the line," said Porterfield. "I haven't seen a replay. Whether or not he did or didn't, it was a great catch."

It was a stunning end to a hard-fought game which was arguably the most important ever played by Ireland. Not just two points were at stake, but their whole campaign to make progress in the corridors of power. Zimbabwe are the weakest Full Member, so an Irish defeat would allow the mandarins a smug smirk and a "not ready yet" stamp on Cricket Ireland's application.

Having lost the toss, Ireland batted first for the first time in the competition and didn't seem any worse for the experience. Although Paul Stirling was out early, and Porterfield was again off the pace, out for 29 in the 21st over, Ed Joyce played one of his most important innings. Scratchy early on, he rode his luck and benefited from some Junior B fielding and catching.

It may take from the quality of the innings but every run was made with style and his 112 was his third ODI century. He was partnered for 138 runs by Andrew Balbirnie, who came in ahead of Niall O'Brien as Phil Simmons changed the batting order for the first time. It seemed an odd move, as O'Brien had the highest strike rate in the competition among Ireland's top seven, but Balbirnie justified it by smacking his first ball for four.

Joyce romped to a 96-ball century, followed closely by Balbirnie's second successive 50, but the senior man fell to Tendai Chatara's slower ball. The middle-order thumped the scoring along, but Balbirnie was growing edgy at the non-striker's end. Having reached 91 in the 44th over, he faced just eight balls in the next five overs and was run out for a career-best 97 trying to keep the strike.

Two more than they made against England in Bangalore, 331-8 was Ireland's best score, and the best by any Associate side against a Full Member, but for long periods it looked not to be enough. The problem, again, is that the seam bowling unit just isn't World Cup class and those who pick the team don't seem to trust the potential replacements.

Cusack was preferred to Max Sorensen and delivered a great opening spell of 7-2-17-1 even before his decisive intervention, but Kevin O'Brien has not been in good sorts with the ball and a boundary was hit off the first ball of half his overs yesterday, a bonus for any batting side. He only bowled a full 10 because Stirling's off-spin was targeted by Zimbabwe and the captain's options were reduced.

Until the dramatic finish it looked as if the diaspora would ruin the run-up to St Patrick's Day, as men called Brendan and Seán conspired to rain sixes on Porterfield's parade. The pair rescued Zimbabwe from 74-4 to add 149 in 21 overs. But when Cusack foxed Taylor for 121, Williams carried on until he reached 96 and that Mooney catch.

Two of Ireland's wins have been narrow, thrilling affairs, in Brisbane and Hobart - an echo from history as the first game recorded in Ireland, in 1792, featured colonial administrators Thomas Brisbane and Robert Hobart. They later served in Australia and are immortalised in those state capitals.

Porterfield's team now have a hectic turnaround, with a 12-hour, 4,000km trip - involving two flights and a coach - to Hamilton in New Zealand where India await on Tuesday. A win there, or even an abandonment, would see Ireland to the quarters, but the forecast is for showers clearing early to dry, light winds. Which means it will all come down to next Sunday morning's game against Pakistan, who surprised South Africa yesterday.