Rory McIlroy has a share of the overnight lead after day one of the BMW Championship, joining Jordan Spieth and Gary Woodland at the top.
The world number one posted a three-under-par 67 at the Cherry Hills Country Club in Colorado, but he could have had the outright lead save for two bogeys in his final three holes.
Spieth carded four birdies on his back nine, picking up shots on holes one, three, six and seven to take a share of the lead, while Woodland started with back-to-back birdies and only had one bogey to mar his round.
McIlroy came into the FedEx Cup play-off event in second place in the points' list, and he will be buoyed by a slow start from leader Chris Kirk, who is tied for 29th after a round of 71.
The benefit for Kirk and other slow starters at the PGA Tour tournament is there will be no cut applied to the 69-strong field - with the top 30 in the FedEx Cup to progress to the season-ending Tour Championship next week.
Tied for fourth after Thursday's play are a group of nine, including 2013 FedEx Cup winner Henrik Stenson.
Stenson was two under through 17 holes, when the siren sounded to end the day's play due to dangerous weather.
The Swede is level with Americans Billy Horschel, Russell Henley, Chesson Hadley, Kevin Chappell, Matt Every, Canada's Graham DeLaet, Germany's Martin Kaymer and Spain's Sergio Garcia - all of whom carded opening-round 68s.
Two shots off the pace, England's Justin Rose began his week in positive fashion with a one-under-par 69 to sit level with eight others in a tie for 13th.
Japan's Hideki Matsuyama, South Korea's KJ Choi, Colombian Camilo Villegas joined Americans Erik Compton, Chris Stroud, Charles Howell III, Ryan Palmer and Jerry Kelly in being under the card at day's end.
Villegas is through 17 holes, while Kelly has another two to play in his first round.
Notables to shoot even-par 70s included Australia's Jason Day, and American major winners Phil Mickelson and Bubba Watson.
US Ryder Cup wildcard picks Keegan Bradley (71), Webb Simpson (73) and Hunter Mahan (75) all shot over the card.