SAN FRANCISCO - World number one Rory McIlroy and Masters champion Jordan Spieth maintained their perfect starts to the WGC-Championship Match Play on Thursday to stay firmly on course for a place in the last 16. Northern Irishman McIlroy, an easy winner in his opening group game on Wednesday, defeated Brandt Snedeker by two up at San Francisco's Harding Park to make it two victories out of two in the lucrative $9.25 million event.

The 25-year-old superstar will now face his 2007 Walker Cup rival Billy Horschel on Friday with a place in the knockout rounds on offer. Horschel joined McIlroy at the top of Group 1 after notching his second win of the tournament, beating Jason Dufner 3&2. Friday's game between McIlroy and Horschel will revive memories of their ill-tempered duels in the Walker Cup eight years ago but the two men have put their animosity behind them and are now on friendly terms.

Second seed Spieth meanwhile trailed early against world number 41 Matt Every but soon turned things around to wrap up a convincing 4&3 win thanks to a red-hot putting display. Spieth will face England's Lee Westwood on Friday with the winner going through to the last 16. Westwood squeezed past Finland's Mikko Ilonen by one up in a nervy encounter that almost went to sudden death.

Westwood had a short birdie putt to seal victory on the 18th but missed, giving Ilonen the chance to force an extra hole. But Ilonen's putt to save the match lipped out leaving Westwood a relieved winner. In other games Thursday, Thailand's Thongchai Jaidee stunned world number five Jim Furyk to keep alive his hopes of qualification for the weekend. The 45-year-old former paratrooper bounced back from his defeat to Germany's Martin Kaymer on Wednesday to sink Furyk 3&1.

With South Africa's George Coetzee downing Kaymer on the first sudden-death hole in the day's other Group 5 game, all four players were left level with one win each after two games. In other games, two-time Masters champion Bubba Watson set up a decisive battle with South Africa's Louis Oosthuizen in Friday's final round of group games after both men notched their second victories. Watson, who demolished Miguel Angel Jimenez 5&4 on Wednesday, was almost as emphatic in dispatching Keegan Bradley, winning 4&2.

 Oosthuizen bagged his second win, eliminating Jimenez in the process, beating the Spaniard by two up. The format for this year's tournament was overhauled to eliminate the possibility of early round exits for top players. The field has been split into 16 groups of four players, with the group winners advancing to the knockout rounds over the weekend.