Illness floors McIlroy and leader Yang

Northern Ireland's young sensation Rory McIlroy has withdrawn from the Sun City Challenge in South Africa due to a stomach virus.

The 20-year-old world No 10, who was making his debut in the 12-man invitational event, had shot a one-over-par 73 followed by a four-over 76 in the opening two rounds, but said he had been troubled by the virus since last week's World Cup in China.

Sunshine Tour communications manager Michael Green confirmed McIlroy, who finished second in the European Tour's Race to Dubai Order of Merit behind England's Lee Westwood, had a "stomach ailment".

McIlroy's third place at the Dubai World Championship saw him climb to 10th in the latest world rankings, making him one of only two players in their 20s – along with Spain's Sergio Garcia – in the top 10.

Meanwhile, the joint overnight leader Ian Poulter is two shots off the pace at the Chevron World Challenge after the second round. Poulter shot a 69 to lie seven under alongside Ireland's Padraig Harrington, who had a 68, and American Kenny Perry, who shot a 65. They trail YE Yang by two shots after he equalled Perry with a 65 at Thousand Oaks in California.

Westwood is on six under after a 67 while Graeme McDowell is four under after carding a 69. Yang, who shot to fame by beating Tiger Woods to win the USPGA in August, said he was "coming down with flu or a fever" during his round.