Defending champion Justin Thomas left the course in a positive frame of mind, though he bemoaned his performance on the back nine at the US PGA Championship.
Seeking back-to-back titles, world number two Thomas opened his defence with a one-under-par 69 in St Louis on Thursday.
Thomas enjoyed a flawless front nine by birdieing three holes but the American star bogeyed twice following the turn without gaining strokes to be five shots adrift of leader Gary Woodland.
"I played well. Obviously, I'm not very pleased with my back nine," Thomas – who won last week's WGC-Bridgestone Invitational – told reporters.
"I've never had my ball end up in somebody else's pitch mark in a bunker before. That was a pretty terrible break on my last hole. Could have cost me one or two strokes.
"It's just unfortunate for someone not to rake it, but it is what it is.
"I played well on the front nine. Had some good holes on the back nine too. Had a couple of putts that didn't quite go in. Had a nasty lip on the 16th hole. Definitely a lot more positives to take the negatives, and I'm in a good position for Thursday."
Thomas added: "I could have shot seven or eight under pretty easily. It's just like any other golf course. I said that at my press conference.
"It's soft enough to where there's going to be some low numbers, but if you're not driving it well, the rough is very difficult and long to where it's hard to make birdies and save par sometimes."
Thomas was grouped with four-time champion Tiger Woods and Rory McIlroy for the opening round at Bellerive Country Club.
Woods – a 14-time major winner – recovered from a rocky start to post a 70, while Northern Irishman McIlroy ended the day alongside the American great.
"It's enjoyable," Thomas said. "I'm worried about what I'm doing, and he's worried about what he's doing, and Rory is worried about what he's doing.
"I've been fortunate enough to where I've played with him enough now that I don't - I don't want to say get wrapped up in it, but the first couple times I maybe played a little bit more attention to what he's doing, but now this is a PGA Championship, and I'm trying to play the best that I can. I'm focused on what I'm doing."
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