Seventy-two holes of struggle await the eventual 2025 U.S. Open winner as Oakmont Country Club is prepared to bare its teeth for a 156-man field all seeking to claim the national championship.

The 125th U.S. Open, the third major of the year, is underway.

Bryson DeChambeau plays his shot from the 10th tee during the first round of the U.S. Open.

The game's stars have dominated the last six majors and most signature events. What will it take for a sleeper to emerge at Oakmont?

Bryson DeChambeau won the second U.S. Open championship of his career last year at Pinehurst, which he sealed by getting up and down on the final hole.

A poor second nine left McIlroy with a 4-over 74 in Thursday's first round at Oakmont.

As the morning wave finishes their rounds, it's J.J. Spaun who sits atop the leaderboard with a stunning 4-under 66.

The U.S. Open began under partly cloudy skies on Thursday at challenging Oakmont Country Club where Bryson DeChambeau hopes to make a fast start to his title defence while tournament favourite Scottie Scheffler was hours from teeing off.

“It is exhausting,’’ Lowry said. “I’m not going to do much else today. Just a lot of rest.’’