Phil Mickelson in jeopardy of missing cut at U.S. Open after carding 8-over 78 in 1st round

Six-time major champion Phil Mickelson said one of the reasons he prefers the new LIV Golf Invitational Series is because of its 54-hole events.

Mickelson will probably only have to play 36 holes in the U.S. Open this week.

Mickelson's return to competitive golf in the United States, and his 52nd birthday, didn't go as planned in the first round of the U.S. Open at The Country Club outside Boston on Thursday.

He carded a 8-over 78 and was tied for 144th place among 154 golfers when he walked off the course.

"I really enjoyed the test; I think it's just a spectacular golf course," Mickelson told reporters in the players' parking lot after the round. "I just really struggled with the putter the first few holes, just like I did last week."

Playing for the first time in the U.S. since missing the cut at the Farmers Insurance Open in late January, Mickelson had bogeys on three of the first five holes and then four-putted from 12 feet for a double bogey on the par-3 sixth.

The highlight of his round came on the par-3 11th, when Mickelson sank an 8-foot birdie, his only one of the round.

But then Mickelson yanked his tee shot into the thick rough on the right side on No. 12, needed two shots to get back to the fairway and carded a double-bogey 6 to drop to 7 over.

Unless Mickelson goes really low in Friday's second round, he figures to miss the weekend in his 31st U.S. Open. 

It is his eighth attempt at trying to become only the sixth man to complete the career grand slam in the Masters era; Jack Nicklaus, Tiger Woods, Ben Hogan, Gary Player and Gene Sarazen were the others. Mickelson has been runner-up at the U.S. Open a record six times.

Mickelson was playing in the U.S. Open after being indefinitely suspended by PGA Tour commissioner Jay Monahan a week ago. Mickelson was one of 17 tour players who competed in the inaugural LIV Golf Invitational Series event in London without a conflicting-event release.