It's Rory v Darren in South Africa

Darren Clarke could delay Rory McIlroy's Masters debut with victory in the star-studded South African Open.

Teenager McIlroy, 19, will tee it up at Augusta National if remains inside the top 50 in the world when the 2008 rankings are finalised on Sunday night.

And that means he will have to watch out for mentor and world No 68 Clarke, who could push him outside the top 50 if he grabs the win he needs at Pearl Valley to guarantee his place at Augusta before the Christmas cut-off.

McIlroy slipped one place to 50th when he missed the cut in last week's Dunhill Championship and would have dropped to 51st if Matthew Goggin had won rather than lost a play-off for last week’s Australian Open.

World No 49 Prayad Marksaeng and No 51 Lin Wen-Tang can also affect McIlroy's ranking as they tee it up in the clashing Volvo Masters of Asia in Bangkok.

But McIlroy can make sure of his invite to Augusta with a top-20 finish in South Africa, where his direct rivals will be Clarke and world No 54 Peter Hanson.

Three of the world's top 10 and five of the top 20 will be in action with Masters champion Trevor Immelman joined by Henrik Stenson, Ernie Els, Lee Westwood and Justin Rose.

Clarke and McIlroy can still qualify for the Masters if they are in the world's top 50 the week before the April 9-12 event.