Two late bogeys saw Rory McIlroy slip back into a share of the lead after round one of the BMW Championship as he chases a first FedEx Cup title.
The world number one came into the third leg of the four-tournament play-off series sitting second in the overall standings and led in Colorado on five under after 15 holes.
But dropped shots on two of his last three saw the Northern Irishman record a 67 and drop back into a share of top spot alongside Jordan Spieth and Gary Woodland.
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"You can see by the scores it's pretty tricky out there," he told Sky Sports 4. "Low scores aren't really too easy to come by so 67 is still a good start even though it could have been a bit better.
"The fairways are firm so even when you're hitting irons and fairway-woods off the tees they're running out and through fairways and into the rough and the rough is thick.
"Then the greens are so firm, the greens have got so much firmer over the past 24 hours and it's really made a huge difference."
Beginning his round on the 10th, McIlroy picked up shots on 12 and 17 and a run of three birdies from the first to the third put him in the driving seat before his two late bogeys brought him back to the pack.
The top 30 in the FedEx Cup rankings after this weekend at Cherry Hills Village will advance to next week's Tour Championship where the points will be reset so every player has a chance of claiming the 10million US dollar (£6.1million) bonus.
And after day one, while the positions within that top 30 had provisionally altered, no player from outside that group was on target to break in, although nine players were still on the course when play was stopped due to risk of electrical activity.
Woodland enjoyed a steady round as he registered four birdies and a bogey while Spieth was a touch more eratic with three blemishes on his card countered by six birdies.
A group of nine players sat a single shot off the lead including European Ryder Cup players Martin Kaymer, Sergio Garcia and Henrik Stenson - who was coming up 18 when the horn sounded to end play.
Justin Rose was in a group a further shot back with Ernie Els, Jason Day, Jim Furyk, Phil Mickelson and Bubba Watson all level par.
Current FedEx Cup leader Chris Kirk was in the group at one over is delighted that his win last week has put him in with a good chance of winning the big prize.
"It's what it's all about," he said. "Being in this kind of position to possibly win that big of a prize is unbelievable and the FedEx Cup is kind of critical for us on the PGA Tour nowadays."
Following his win at the Deutsche Bank Championship, many thought Kirk may have been handed a Ryder Cup wild card by United States captain Tom Watson but the skipper instead went with Hunter Mahan, Keegan Bradley and Webb Simpson.
But Kirk claims that was not a huge disappointment, and said: "I pretty much was still on cloud nine coming off such a big win and, as I've said all along, those guys who finished in the top nine are the ones that have control of them being on the team.
"Beyond that, captain Watson has the right to do whatever he feels like he wants to do."
Mahan experienced a poor first round as he shot a five over 75 while Patrick Reed, who qualified for the American team to play at Gleneagles, was seven over.