Oosthuizen: 'It was a battle to keep calm. Having such a big lead was difficult'

With the first line of his victory speech Louis Oosthuizen wished a happy 93rd birthday to his former president Nelson Mandela last night and then went on to describe his amazement at winning the Open by the second biggest margin in 97 years.

"It's unbelievable – just amazing," said the South African after collecting the winner's cheque for £850,000. "It's probably going to hit me tomorrow or the week after. I felt like I played well all week and the biggest goal for me was to stay cool."

While that is exactly how he looked on the way to his seven-stroke triumph, the 27-year-old revealed that he did have to keep his nerves his check. "I'm glad I had a seven-shot lead on the 18th," he said. "I think I cramped up a bit with the putter on the last as well. It was a battle for me to keep calm round this course. I'd like to have kept the record of not going in the bunker [as Tiger Woods did in 2000), but I went in one on the 14th. It became a bit difficult having such a big lead."

Oosthuizen's stunning win was welcomed by his countrymen and European Tour colleagues alike. Retief Goosen is now one of four South Africans to win majors this century and said he was not "too surprised" to see the professional from the Western Cape prevail. "Shrek is on the move," he said referring to Oosthuizen's nickname. "We knew he had a lot of talent. He grew up in an area that's very windy, so for him these conditions are normal. The guy's got one of the best swings on tour. I think he'll be around for many years to come."

Ian Poulter agreed with this assessment. "Maybe I wouldn't have backed him at the start of the week but a lot of us on the European Tour would have thought of Louis as an underachiever," said the Englishman. "When you swing it that well, hit that long and straight then whenever you have a good putting game your going to have a chance. He probably did have the best of the draw in the first two rounds, but he was faultless on the weekend. It's obviously great for Louis but also great for the European Tour."

Meanwhile, the runner-up took consolation from the fact the winner had performed so expertly. Lee Westwood, who lost by one after a closing bogey at Turnberry last year and was second to Phil Mickelson at The Masters in April, is not going to be too hard on himself. "I know what I've got to do – improve," he said after his 70. "I'm showing a lot of consistency, but it's not quite good enough. I keep putting myself in position and in contention – that's all I can do. The pin positions were tough. This is not an easy course when there's a 20mph wind blowing. And Louis is obviously playing really well."

In reality, Paul Casey will spend far more time than Westwood considering the might-have-beens after starting four shots off the lead and slumping to a 75. Rory McIlroy also confessed last night that he, too, was harking back to the low moments despite finishing the weekend 69-68 to climb back up to a tie for third. Yet he had started off with a record-equalling 63 and followed it with an 80 in Friday's 40mph winds.

"I couldn't help but think about it going up the last hole," said McIlroy. "You know, 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 it's not going to give me nightmares. I'll wake up in the morning and just look at the fact I was 16-under for three rounds around St Andrews in the Open. I had just one bad round. It's fine."