Rory McIlroy said he is in a "good spot" mentally after making a strong start to his quest for U.S. Open glory.
The four-time major winner headed to Brookline on the back of a superb victory at the Canadian Open last weekend and opened up with a three-under-par 67, a score that was enough for the co-lead when he finished his round.
McIlroy made a bogey on his final hole to put a slight dampener on things, but the Northern Irishman feels in good spirits as he bids to end an eight-year wait for a major trophy.
"I think [winning the Canadian Open gave me] comfort, more than anything else," said McIlroy, whose triumph in Canada was his 21st on the PGA Tour.
"Knowing my game is in good shape, knowing that when I had to answer the call, make some birdies or do something, I was able to.
"I feel like playing 72 holes in a U.S. Open is playing under pressure the entire time, even though the tournament doesn't really start until the weekend.
"But yeah, [it gave me] comfort with my game, mentally I think I'm in a good spot, and I showed that out there today, just trying to keep myself going.
"Overall, my wedge play was pretty good, I gave myself plenty of chances. Really nice at 17. It was a little skip up the hill, I could see it pitch into the hill and zip back down the green. I hit the putt at seven a little firm, but it was nice after a couple of par saves to see another birdie go in."
Also among the early finishers was defending champion Jon Rahm, who sank a 21-yard putt for birdie on the 18th, ensuring he finished his first round with a one-under 69.
Having endured a frustrating back nine, Rahm spoke of his relief at seeing one drop.
"I played a really good first eight holes besides the bogey on three," he said. "I played really, really solid, and then the wind picked up and it was a bit of a struggle, so to finish with that birdie makes me really confident and it's a really good way to start.
"I didn't see anything go in all day, and to see that one curl in after a wayward tee shot, I got a little lucky, got a great drop and I was able to make that birdie, it's a good feeling to finish like that.
"It got a little difficult out there, I hit a lot of bad iron shots [on] the last 10 holes, so to make that putt felt really good."