Open leader Louis Oosthuizen reveals his debt to Ernie Els

A decade ago Oosthuizen received crucial backing from Els' Foundation, which supports young golfers who lack the funds to make the most of their talents.

At St Andrews today he fired a five-under-par 67 to take the second-round clubhouse lead on 12 under, leaving him in the perfect position to reward his mentor, who won the 2002 Open at Muirfield.

Oosthuizen said: "Getting into golf is very expensive. My dad is a farmer, and in the early years things weren't going that great on the farm. But when I was 17, I managed to become a member of Ernie's Foundation in South Africa and it was unbelievable what he did for me, helping with expenses and things like that.

"He's such a good mentor, a great, great guy to be around. Without him, and those three years I was with his Foundation, I wouldn't have been here."

In fact, the 27-year-old struggled for some time to make a living from golf.

A member of the South African team that won the World Junior Championships in 2000, Oosthuizen didn't triumph on the European Tour until the Andalusian Open in March.

He failed to make the cut in his three previous Open appearances and also suffered that fate in his last five Majors.

Oosthuizen said: "It was a matter of not believing in myself but the win earlier in the year in Spain got my confidence going. Everyone was telling me you've got the shots, you're playing well', and that win finally got my mind set in a different way. Now I'm reading it really nice."

Oosthuizen — nicknamed Shrek' by his mates because of his gappy front teeth — certainly read it nice during a morning which saw glorious early sunshine eclipsed by cloud carrying heavy, driving rain.

Three successive birdies from the fifth hole gave him momentum, and while he dropped two shots on the back nine he made them up and grabbed a bonus birdie at the last.

Oosthuizen said: "I was trying to go shot for shot and make the best possible swings every time. You don't really want to get ahead of yourself, especially not on this golf course.

"I think it's very important staying in the moment and thinking properly about what you're doing out there, and not making thinking errors."

The Open has a habit of turning outside contenders into champions —witness the unexpected successes enjoyed by Paul Lawrie, Ben Curtis and Todd Hamilton in recent years.

"St Andrews is where golf started," said Oosthuizen. "To win the Open is everyone's dream, but to do it at St Andrews? I never thought that could happen to me."

His round left him three ahead of overnight leader Rory McIlroy, who parred the first three holes of his second round. Paul Casey will resume tomorrow six off the lead, a gap that might have been closer had he not carded a triple-bogey seven at the infamous 17th Road Hole'.

After signing for a three-under 69 Casey explained: "It was a pretty easy seven! It wasn't a great tee shot in the left rough and when I got down there I tried to go out sideways.

"The club just went straight underneath the ball. For my third shot I had to go backwards down the fairway and then from there up to the green, and a few more whacks.

"To be honest, I'm not even that frustrated with what happened on 17. If you had told me I'd be in the clubhouse on six under I would have bitten your arm off, especially given the wind and the pouring rain."