ST. ANDREWS, Scotland, July 19- Rank outsider Louis Oosthuizen won the British Open on Sunday, capturing golf's biggest prize by a stunning seven strokes with an accomplished display of front-running.It was the biggest winning margin in the world’s oldest and most prestigious tournament since Tiger Woods won here by eight strokes in 2000.
The 27-year-old South African, a 200-1 betting shot on Wednesday, started the day on 15-under par, four strokes ahead of England’s Paul Casey and with the rest of the field already left trailing in his wake.
Plotting his way around the Old Course links, Oosthuizen was never really threatened as he carded a closing 71 for a 16-under total of 272.
The runner-up spot, a distant seven strokes back, went to England’s Lee Westwood who closed with a 70 with three players in a tie for third a stroke further back – Rory McIlroy (68), Henrik Stenson (67) and Casey (75).
"It’s unbelievable," said Oosthuizen.
"It was difficult having such a big lead to keep calm and focussed, but I kept calm all the way.
"I’m glad I had eight shots on 18! I think I cramped up a bit with the putter. It’s just amazing."
It was just the second top-level tournament win of Oosthuizen’s career after the lowly Andalucia Open in March and it came on a day of celebration back home for Nelson Mandela’s 92nd birthday.
Ranked 54th in the world coming into St Andrews, Oosthuizen was the fourth South African to win the Open after Bobby Locke (1949, 1950, 1952, 1957), Gary Player (1954, 1968, 1974) and Ernie Els (2002).
It was the biggest upset win in an Open at the Home of Golf since American Tony Lema won on his debut at the Old Course in 1964.
Oosthuizen carded superb rounds of 65, 67 and 69 to set up his winning position and only Casey with rounds of 69, 69 and 67 managed to hang onto his coattails.
Casey had an immediate chance to crank up the pressure on his more inexperienced playing partner when he hit his approach to within five feet at the first, but he pushed his putt wide.
The Englishman then bogeyed the second to provide Oosthuizen with the perfect start as he himself held firm with two pars to stretch his lead to five.
Casey had another chance to pull one back at the par-five fifth but again failed to sink a makeable birdie putt.
Ahead of them, no-one among the chasing pack was able to mount a charge.
Martin Kaymer of Germany, who had been in third place overnight at eight over, bogeyed the first, while Stenson of Sweden, Westwood and Alejandro Canizares of Spain all parred the first four holes when it was birdies they needed to stand any chance of reeling in the leader.
Casey did cut the lead to three when he birdied the sixth and Oosthuizen had his first of two bogeys on the day after over-hitting his tee-shot at the par-three eighth.
But on the next hole, Oosthuizen drove the short, par-four green and sunk a 30-footer for a crucial eagle, while Casey had to settle for a birdie. The lead was back to where it started at four over.
When Casey clattered his drive into thick gorse on the tricky par-four 12th minutes later and limped off with a triple bogey seven to Oosthuizen’s birdie three, it was all over.
Westwood eventually passed a fading Casey for the runner-up slot making it four top-three finishes in the last five majors.
"Whether I won the tournament today was in the hands of other people," the European number one said.
"Louis has obviously played great and thoroughly deserves to win. So there’s not even any real disappointment.
"If you get close and you lose, then there’s disappointment, but I didn’t even get within eight shots today."
Casey also paid tribute to the South African, who only went in one of St Andrews’ many bunkers all week.
"That was an unbelievable performance," he said.
"He was very calm, played wonderful golf, and all credit to him. I’m disappointed, but the emphasis has to be on that performance, because that was fantastic."
World number one Woods, whose hopes of an unprecedented hat-trick of Open wins at St Andrews evaporated with a disappointing 73 on Saturday leaving him 12 shots off the lead, had two double-bogey sixes on the front nine.
He battled back to finish with a par 72, but at three under for the tournament he was way back in a tie for 23rd place, his dreams of a 15th major well and truly shattered.
"I drove it great all week, hit my irons pretty good, and I did not putt well except for the first day," he said.
"I believe I had like nine three putts for the week, so consequently I’m pretty far down the board."
Ulster young gun McIlroy, who opened with starkly contrasting rounds of 63 and 80, finished strongly with a 68 which left him tied for third.
"I couldn’t help but think about Friday (80) going up the last hole there," he said.
"If I had just sort of stuck in a little bit more on Friday and held it together more, it could have been a different story. But the other three rounds I played very, very solidly."