Lee Janzen recorded 17 points under the modified Stableford scoring system to grab a slim lead over Chris Riley after the first round of The International in Colorado.
Janzen, who is playing for the first time in a month, missed the cut in five of his previous eight starts but blamed his "physical wellness," not his mechanics.
"Energy-wise, I just needed to lay off the things I was eating and detox for a while," said Janzen, a two-time US Open champion who won here in 1995.
"And I've increased my energy a bit and feel a lot better."
Janzen has sworn off sugar, dairy products, bread and "anything that has yeast in it."
"Maybe I'll do a 100-yard dash when the tournament is over on Sunday!"
With 10 points through 16 holes, Janzen finished eagle-birdie to cap a bogey-free day. His eight-under-par 64, on a day when players were allowed to lift, clean and place, would have matched his best round of the season.
Finishing on the front nine, Riley closed with five straight birdies to end his day with 16 points. He had nine birdies and two bogeys for the day.
Rory Sabbatini of South Africa is alone in third with 14 points, totalling eight birdies and two bogeys. Scott McCarron is fourth with 13 points, one ahead of Jose Maria Olazabal of Spain, Mark O'Meara, Brent Geiberger and Tom Pernice Jr.
David Duval and Phil Mickelson were among eight players to finish with 11 points. Duffy Waldorf had 11 points through 16 holes before play was called off.
World number one Tiger Woods is skipping the event and next week's Buick Open. He will seek his third straight PGA Championship title in two weeks.
Forty-two of the 144 players in the field could not finish the first round, thanks to a rain delay of nearly three hours.
PA