World No 1 Luke Donald heads a star-studded group including two former world number one golfers in the Nedbank Golf Challenge invitation tournament starting Thursday. Fellow Englishman and last year's champion Lee Westwood, currently ranked third, and world number four Martin Kaymer from Germany are also bound for Sun City, the casino resort northwest of Johannesburg. Both have ranked number one in the past. "I think it speaks volumes for the status of the Nedbank Golf Challenge that for the second year in succession we have been able to secure the world?s number one golfer for our tournament," said director Alastair Roper. The trio will be joined by the likes of Northern Ireland's Graeme McDowell, winner of the 2010 US Open as well as fellow Ulsterman and current British Open champion Darren Clarke. Westwood won the title by eight strokes last year after shooting 68 in the final round. The 38-year-old struggled for form this year though he finished third in the US Open, losing to world number two Rory McIlroy from Northern Ireland. McIlroy preferred the Hong Kong Open rather to playing in South Africa. South Africa's only hope for the "African Major" lies with Charl Schwartzel, who shot to prominence after a surprise win at this year's Masters. Possible dark horse is Italian Francesco Molinari -- younger brother of Edoardo -- who last year beat Westwood to take the WGC-HSBC Champions event in Shanghai. Molinari replaces veteran Dane Thomas Bjorn, the three-time tournament winner this year had to withdraw from the tournament because of a neck injury. The elite 12-man field will compete for $1.25 million, surpassed only recently by the Shangai Masters' winning prize of $2 million. "I think this year?s field showcases the amazing depth in world golf at present," said Roper. "In the current global golf climate and with the leading tournaments of the world vying strongly for the attention of the top players, I am very pleased with the field we have secured." "The fact that the Nedbank Golf Challenge still attracts the best golfers in the world after three decades reaffirms the event?s status as Africa?s Major." Andy Scott, head of group sponsorships at Nedbank, was also delighted with the turnout. "It is an achievement we are tremendously proud of," he said.