U.S. Open golf: Adam Hadwin leads after first round; Phil Mickelson struggles

June 16 (UPI) -- Canada's Adam Hadwin, who wasn't officially competing in the U.S. Open until eight days ago, held a one-shot lead at the major tournament after Thursday's first round at The Country Club in Brookline, Mass.

With the focus moving away from the rival LIV Golf series, Hadwin opened with a 4-under 66 on a breezy day at Brookline. He rattled off three consecutive birdies to finish the front nine in 31, and he carded just one bogey on the back nine for his best score ever in a major.

His previous low score in a major was 68 on three separate occasions, most recently in the first round of the 2020 PGA Championship at Harding Park.

"I know this is the U.S. Open. I know it's difficult," Hadwin said. "I think in the past I may have played too cautiously because it was a U.S. Open and said, 'I need to hit it up here and do that.' Today, I treated it like every other tournament.

"I got a wedge from 100 yards, I'm going to be aggressive. That was probably the biggest key to my success."

The 34-year-old Hadwin, who was the first alternate out of the Dallas section and got in the tournament when Paul Casey withdrew due to a back ailment, ended the round one stroke ahead of Rory McIlroy, Matthys Daffue, Callum Tarren, Joel Dahmen and David Lingmerth, all of whom shot 67s.

Dustin Johnson and Justin Rose were among the seven-man group tied for seventh at 2-under par.

At the opposite end of the leaderboard was Phil Mickelson, who opened with an 8-over 78 to leave him in danger of missing Friday's cut line. He had just one birdie in the first round against five bogeys and two double bogeys.

Mickelson and Johnson were among 13 players at the U.S. Open who participated in the Saudi-funded LIV Golf circuit last week. In response, the PGA Tour suspended those members prior to the inaugural LIV Golf event.

Thursday's first round at the U.S. Open, however, returned the focus to the action on the course and away from the rivalry between the PGA Tour and LIV Golf that has dominated headlines in recent weeks.

Only 25 players out of the 156-man field finished below par in the first round at Brookline, which featured moderate wind and lots of cloud coverage. Seven of the top 13 came through qualifiers.

The U.S. Open will run Thursday through Sunday at The Country Club. The winner of the event will receive $3.15 million of the tournament's $17.5 million prize purse.