Thomas Detry fired seven birdies in a six-under par 65 on Saturday to push his lead to five strokes heading into the final round of the Phoenix Open in pursuit of his first US PGA Tour title.
"I'm playing some great golf," Detry said. "I kind of feel like I'm ready to handle Sunday properly now."
The Belgian, leading by two to start the day, built an 18-under par total of 195 at TPC Scottsdale and was five clear of a quartet of players led by three-time major winner Jordan Spieth.
Spieth, making his second start after a five-month absence in the wake of wrist surgery, carded a four-under 67 and was joined on 200 by Denmark's Rasmus Hojgaard, who carded a 65, American Daniel Berger, who signed for a 66, and Michael Kim, who carded a 68.
American Maverick McNealy was alone on 201 after a bogey-free eight-under par 63 that matched the low round of the tournament.
Detry, ranked 58th in the world, said he felt a few butterflies to start the day, but they were quickly settled with a birdie at the first, where his nine-iron approach left him less than four feet from the pin.
He added birdies at the third, fourth and fifth and bounced back from a three-putt bogey at the seventh with a nine-foot birdie at the eighth.
After birdies at 14 and 17, he closed his round with an 18-foot par-saving putt at the 18th, where his tee shot had left him an awkward lie in a fairway bunker.
"Getting off to such a good start was kind of the dream today," said Detry. "I don't think I missed a shot in the first five, six holes.
"I was trusting my game and trusting my ball flight and kind of seeing the shots. And I've been putting well, which helps."
Spieth, who had left wrist surgery late last year after struggling with pain through two seasons, had four birdies without a bogey and also finished with a great par save after finding two bunkers at 18.
"I thought it was big," he said of the save. "I knew that I hadn't made a bogey in a while so I wanted to keep that streak alive."
Spieth said he wasn't swinging as well as he did on Thursday, but he was pleased to be able to produce a solid score.
"But tomorrow I'm going to have to hit more fairways because I'm going to have to hit it closer to try to catch Thomas," he said.
Hojgaard had pulled within three strokes of Detry after a nine-foot eagle at the 13th. But the Dane, who has five DP World Tour titles, found the water at the 15th on the way to a double bogey.
He kept himself in the hunt for a first US victory with birdies at 17 and 18.
"It was nice to play the last three holes well," Hojgaard said, adding that it was key to "try to embrace" the rowdy crowds at a tournament known for its party atmosphere.
"It was good today," he said. "I really enjoyed it."