World No. 1 Tiger Woods, without a victory since March, equalled the course record by firing a nine-under-par 63 to grab the lead after the first round of the 100th Western Open on Thursday.
Woods, playing his last event before the British Open in two weeks' time, carded his lowest round of the year.
He went out in a four-under 32 after starting at the 10th and then added five birdies on his inward nine, including four in the last five holes.
Vance Veazey was in second place on 64 at Cog Hill Golf and Country Club's Dubsdread course. World No. 7 David Toms, who won the FedEx St Jude Classic last Sunday, continued his excellent run of form by shooting a 65.
Title holder Jerry Kelly was fourth on 66. US Masters champion Mike Weir of Canada, Cliff Kresge, Jason Gore, Chad Campbell, Heath Slocum and Brian Bateman were four strokes off the pace on 67.
Woods, 27, who won here in 1997 and 1999, posted an eagle, eight birdies and one bogey in what he called his best round in four months.
"Different circumstances but I really played probably the same way at the World Matchplay [in March]," he told reporters. "But obviously, it's matchplay, so you have two totally different mind-sets."
His matchplay victory at Carlsbad, California was followed by another win at the Bay Hill Invitational three weeks later, but he said he had not suffered a slump in form since then.
"See, if you've been following what I've been saying the last few tournaments I've played in, I'm very close," he said.
"It's just a matter of the things I'm working on, for them to come around. You have to be patient.
"I hit a lot of good shots today. It's a lot of fun when you hit shots that flush and that solid, and it's awfully nice to get rewarded by making some putts," said Woods, one of the late starters on Thursday.
"I hit some good putts with some nice speed that went right in the hole. It was a good combination."
The world No. 1's round was interrupted halfway through by a thunderstorm.
Three of the top four scores, by Woods, Veazey and Kelly, were completed after the rain delay.
"When we started out playing today, to be in the top 10 you had to shoot five-under-par, and I think that's kind of where I stayed at, so you can see it wasn't very firm to begin with, and then with the rain it became even softer," Woods said.
Veazey, 38, a product of the Nationwide Tour, finished 10 shots behind Toms last week and carried on the momentum with a career-best 64.
World No. 5 Vijay Singh of Fiji and No. 6 Jim Furyk, the US Open champion, were on one-under 71. No. 9 Phil Mickelson returned a 70.