Rory McIlroy insisted his rib injury caused him no problems at the U.S. Open, putting his poor start down to rustiness and bad timing.
The Northern Irishman, playing his first tournament in a month, carded a six-over 78 at Erin Hills on Thursday.
McIlroy was two under through two holes, but followed that with four bogeys and two double-bogeys.
The four-time major winner was unwilling to use his injury as an excuse after hitting just five of 14 fairways in his first round.
"I feel great. That's all totally fine. I was hacking around in the rough out there and didn't feel it one bit. So, no, that's totally fine," McIlroy said.
"Just timing was a little bit off, and that was it. Yeah, just really bad tee shots which led to obviously not being able to give myself many looks for birdies."
McIlroy has played just six tournaments this year and said rustiness cost him in Wisconsin.
He said: "A little bit of rust. A bit of rust, timing. Timing was a little off.
"I started missing some left on the course and tried to sort of correct it on the way in and missed a couple right.
"So a little bit of timing, and a bit of rust as well."