Colombia's Camilo Villegas powered into the lead with an opening five-under 65 after the rain-hit first round of the BMW Championship in St Louis.
Villegas, 26, was one shot clear of US Ryder Cup duo Steve Stricker and Kenny Perry, as well as Tim Herron, Andres Romero and Stuart Appleby.
In a group two strokes adrift were Ernie Els, Sergio Garcia, Anthony Kim, Phil Mickelson and JB Holmes.
Padraig Harrington fired 69, while Vijay Singh shot a level-par 70.
Scotland's Martin Laird was also one under, but England's Brian Davis carded 75 for five over.
The BMW Championship, which is the third and penultimate event of the PGA Tour play-off series, saw the first day washed out after the remnants of Hurricane Gustav swept across Missouri.
The field will play 36 holes on Saturday to get the event back on track for a Sunday finish.
Open and USPGA champion Harrington has missed the cut in his past two events.
"I'm a lot fresher and ready to go. There was a lot more there today than the last two weeks"
"There's a bit of a kickback from that and you have to accept it," he said of the post-major letdown.
"I'm experienced enough in this game to understand there are ebbs and flows.
"The main thing is to make sure you peak at the right times during the year and I've got better doing that.
"It's inevitable if you do try and peak you'll have a bit of a dip afterwards. I'm trying to hang on (for the Ryder Cup).
"My schedule was set out this year so I would peak again for the Ryder Cup but I didn't envisage having so much drama in the middle of the season.
"It's one thing to win one major. To back it up with another, you really are knocking your systems down, but they are coming back.
"I'm encouraged by this week. I've been a lot fresher and ready to go. There was a lot more there today than the last two weeks. If I'd shot 68 I would have been very happy with my day but 69's okay.
"I'm keen to play, which is a good sign. I'll have a week off next week and I should be ready for the Ryder Cup."
Other US players in St Louis who will compete in this month's Ryder Cup include Justin Leonard (-1), Hunter Mahan (-1), Jim Furyk (level), Boo Weekley (+1), Stewart Cink and Chad Campbell (both +3).
US-based Swede Carl Pettersson, who was overlooked for one of the European wildcards by captain Nick Faldo, carded 72 for two over.
Fiji's Singh, 45, has one hand on the FedEx Cup trophy and the $10m (£5.6m) bonus that goes to the play-off champion after winning the first two events.
The top 30 qualifiers on the standings after the BMW Championship will compete at the Tour Championship later this month.
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