(CNN) -- South Africa's Louis Oosthuizen claimed his first major title with a runaway seven-shot victory in the British Open at St.Andrews.
The little-known Oosthuizen was a 200-1 shot with the bookmakers before the start of the tournament but played like a true champion in the final round as his challengers fell away.
"It's unbelievable," Oosthuizen told BBC Sport. "It was difficult having such a big lead to keep calm and focussed, but I kept calm all the way. It's just amazing."
His one-under-par 71 gave him a 16-under total of 272 with England's Lee Westwood continuing his consistent form in the majors by finishing second on nine-under 279.
Paul Casey, first round leader Rory McIlroy of Northern Ireland and Swede Henrik Stenson were tied for third a further shot behind.
South Korea's Jin Jeong finished as the leading amateur on four-under-par, closing out his tournament by holing a spectacular eagle putt on the 18th.
England's Casey began the day as Oosthuizen's closest rival, four shots behind and cut the gap to three when his playing partner bogeyed the eighth.
But the leader responded in magnificent style at the par-four ninth as he holed a 35-footer for an eagle to Casey's birdie.
The final turning point came at the par-four 12th where Casey racked up a triple bogey seven and suddenly Oosthuizen had an eight-shot lead.
He was never going to relinquish such an advantage, his only dropped shot coming home at the notorious 17th Road Hole.
The 27-year-old sealed victory with a par on the final hole, adding to his breakthrough win in the Andalucia Open on the European Tour earlier this year.
He had trailed McIlroy by two shots after a first round 65, but his early start on the second day spared him the worst of the gale-force winds which battered the Old Course.
A superb five-under 67 left him with a five-shot halfway lead and third round 69 maintained his challenge going into the final day.
He joins Bobby Locke, Gary Player and Ernie Els as South African winners of the Claret Jug, particularly fitting on the day Nelson Mandela celebrated his 92nd birthday, with Oosthuizen sending his own public greetings in his acceptance speech.
McIlroy, who carded a disastrous 80 in the second round, again showed his mettle to delight the galleries with a four-under 68, but Germany's Martin Kaymer, third overnight, slipped to a 74.
That left him in a tie for seventh with the best of the Americans, Sean O'Hair and Nick Watney, on six-under.
World number one Tiger Woods finished in a tie for 23rd at three-under after a final round 72, with arch-rival Phil Mickelson tied for 48th at one-over.