Justin Thomas carded eight birdies while shooting a 6-under 65 on Saturday to hold a one-shot lead after three rounds of the World Golf Championships-Mexico Championship in Mexico City.
Thomas stands at 15-under 198 after three trips around Chapultepec Golf Club. He is one shot ahead of Patrick Reed and South Africa's Erik van Rooyen.
Spain's Jon Rahm, Northern Ireland's Rory McIlroy and Bryson DeChambeau are four shots back in a tie for fourth.
Rahm set a course record with a 10-under 61.
Thomas bogeyed the first hole and also the 18th when he missed a short par putt. In between, he was strong with three birdies on the front nine and five on the back nine.
Thomas, who hit 14 of 18 greens, is looking for his third victory of the season.
Reed and van Rooyen each shot 67 with the former having a shot at 66 before a bogey on 18. Reed had one other bogey and made six birdies.
Meanwhile, van Rooyen started well with a birdie and an eagle on the par-4 No. 2 before losing momentum with bogeys on Nos. 5 and 7. On the back nine, he had four birdies and a bogey during a five-hole stretch from Nos. 11-15.
Rahm's stellar round was highlighted by a hole-and-one on the par-3, 17th hole. He knocked the tee shot in from 158 yards for his second ace on the PGA Tour.
Rahm also had birdies on six of the first seven holes and had nine birdies overall. His lone blemish was a bogey on the par-4, eighth hole.
Rahm hit 16 of 18 greens and needed just 25 putts during his round.
"I think a lot of us like to talk sometimes about how unlucky we get," Rahm said afterward, "and I think today was one of those days where I got fortunate. I hit the right shots and I got the right bounces, and I took advantage of it."
McIlroy had five birdies and two bogeys while shooting 68. None of his birdies occurred over the final six holes with a bogey on No. 14 also hindering his chance to move closer to the lead.
DeChambeau had an eagle of the par-4, second hole but gave the shots back with a double-bogey on the par-5, sixth hole with shooting even-par 71. He also had three birdies but bogeyed three of the final six holes.
Englishmen Paul Casey and Tyrrell Hatton are tied for seventh at 203 after each shot 66.
Gary Woodland (65 on Saturday), Kevin Na (65) and Japan's Hideki Matsuyama (71) are tied for ninth, six shots behind Thomas.
Defending champion Dustin Johnson shot 67 but is well off the pace. He is tied for 41st at 1-over 214.
--Field Level Media