A four-under round of 66 gave South Africa's Tim Clark a two-shot lead going into the final round of the Crowne Plaza Invitational.
Australian Jason Day, Steve Stricker and fellow American Steve Marino, who shot the best round of the day - an eight-under 62 - are all on 15 under.
Fijian Vijay Singh is a further two shots behind following his 69.
England's Paul Casey, fresh from his win at Wentworth, is six shots behind the leader after carding a 66.
Clark ended his round with a birdie to give himself a great chance to land his first victory on the US Tour having finished a runner-up on six occasions.
"I played great golf today and need to try to keep that going," he said.
"Today was a good solid round. I did what I wanted to do but guys came at us with some good rounds so it's going to be close tomorrow."
The South African began the day one shot behind playing partner Stricker before making five birdies, dropping just one shot on the 7th, to leave himself leading the pack.
But the honour of round of the day fell to Marino, who carded eight birdies in total, coming home in just 30.
Casey, up to third in the world rankings following his PGA Championship victory and searching for his second US win this season, was five under for his round after 15 holes but bogeyed the par-three 16th following a poor tee-shot.
Fellow Englishmen Luke Donald, who made 67, and Ian Poulter, with 65, are on 10 under.