There are some golfers who agonise for an aeon about the rights and wrongs of using a belly putter. Not Brendan Walton. He was but a whip of a lad, aged eight, when his uncle Philip, the Ryder Cup hero of 1995, first used the contraption. Imitation is the greatest form of flattery, and the young Walton decided that would be the way that he too would putt.

He did, and he still does.

And, yesterday, on the sort of beautiful sunny day stolen from an old summer's calendar, Walton - a 20-year-old from Malahide, who has just completed a golfing scholarship studying sports management at UCD and who plays his golf out of The Island - produced the biggest upset of the South of Ireland amateur championship over the Old Course at Lahinch when he defeated the reigning Irish Close champion Shane Lowry.

It was a fourth-round match that Walton, a former boys' interprovincial for Leinster, slowly acquired a hold on. One down through three holes, and level after birdieing the par-five fourth hole known as Klondike, the Dubliner went ahead for the first time by winning the sixth and remained one-up at the turn before producing an assault that saw him win the 10th in par, the 11th in par and the 13th in birdie where the drove the green on the 279 yards par four and two-putted to move four-up.

Although Lowry threatened a fight back by winning the 14th when Walton's drive found a fairway bunker, there was to be no capitulation. Walton closed out the match on the 16th. Of his use of the belly putter, Walton observed: "You get a nice roll with the ball with the long putter on these greens."

Hardly a week goes by when Walton doesn't play a round of golf with his uncle. What has he learned? "Philip gives me bits of advice. Like, in matchplay, he told me, 'you have to bite them, don't show them any mercy' and I knew I had to do that against a player like Shane. He's capable of throwing four birdies in a row at you."

Simon Ward, the defending champion, avoided such pitfalls as befell Lowry but still had to dig deep to stay in the championship. The Co Louth clubman had an early scare against Kilkenny's Gary Nugent when he was two down at the turn but recovered to record a 2 and 1 win in advancing to the last 16. At this stage, he looks to be the man to beat.

However, there were other impressive performances, and none more so than the continued winning ways of Darren Crowe - a beaten finalist the last two years - who didn't lose a hole in his two matches yesterday. His next match could be a tougher assignment, against American teenager Brendan Tracy who plays off a plus-four handicap.

A 19-year-old student at the University of Maryland, the New Yorker - who plays out of the famed National Links near Southampton on Long Island - is no stranger to Lahinch. His father, James, is a lifetime overseas member and has taught his son the course's nuances.

Brendan won the JB Carr junior tournament here in 2004 and sees a similarity between both courses separated by the Atlantic. "They're both pure links," said Tracy of National and Lahinch. "You've got to keep the ball underneath the wind and to make putts. My philosophy is to go out and have fun, to make fairways and greens and not to give your opponent the hole. You've got to make them beat you with birdies."

It's a game plan that so far has served him well.