Nirat used three birdies and an eagle in 11 holes to move to 9 under, two strokes ahead of Englands Simon Dyson, Thomas Bjorn of Denmark and Singapores Lam Chih Bing. Play was largely rain-free Saturday after being delayed the first two days of the tournament because of lightning.
Nirat said he was 95 percent sure he would win the tournament Sunday.
Some of golfs biggest names moved back into contention Saturday with solid, if truncated, performances. American Phil Mickelson, who lost his world No. 2 ranking to Spains Sergio Garcia last week, was 4 under through 14 holes, leaving him four strokes off the lead.
Im happy with the way I played, Mickelson said. Ill need to make a few birdies tomorrow as there are a lot of good players in front of me.
Irelands Padraig Harrington, winner of two majors in 2008, shot a 5-under 66 and is also four shots back, along with South Africas Ernie Els, Rory McIlroy of Northern Ireland and Indias Jeev Mihha Singh.
Lam, seeking to become the first Singaporean to ever win the $5 million tournament, said boisterous local fans have helped inspire his play.
The support from the crowd is awesome, Lam said. Its unbelievable how good the galleries are here this week.