Phil Mickelson took advantage of benign conditions on Scotland's west coast Thursday to fire a 63 in the opening round of the British Open, matching the lowest score ever posted in one of golf's four major tournaments. 

Mickelson had a chance at a 62, but his 16-foot birdie putt on the 18th hole at Royal Troon veered to the right, slid around the edge of the cup and stayed out. 

"All those highlights," Mickelson said after the round, "and I feel like crying."

Mickelson joined 26 other players who have shot 63 in major championships. The last to achieve the feat was eventual champion Jason Dufner at the 2013 PGA Championship. Intriguingly, only six of the previous 26 players have gone on to win the tournament. 

The last man to shoot 63 at a British Open was Rory McIlroy at St. Andrews in 2010. He finished in a tie for third place behind eventual champion Louis Oosthuizen. 

With most of the leaders in the clubhouse Thursday, Mickelson (-8) led fellow American Patrick Reed and Germany's Martin Kaymer by three shots. Eight others, including defending Open champion Zach Johnson, were a shot further back at -4. 

U.S. Open champion Dustin Johnson  played a round that usually gets rewarded at a U.S. Open — 14 pars, two birdies, two bogeys. Except this was the British Open, and the conditions were never easier at Royal Troon.

Johnson blasted driver on the opening hole toward the sea and made bogey. He played the par 5s in even, finishing with even-par 71.

Two-time major champ Jordan Spieth also shot 71 after a round that saw him struggle on the greens, including two missed 10-foot birdie putts on his first two holes.

When asked what was wrong with his putting, Spieth smiled and said, "That's a question I almost never get asked. So because of that, I'm not thinking much of it."

World No. 1 Jason Day continued his year-long trend of poor starts in majors, shooting a 73.

"I'm already missing greens anyways," he said. "And if I'm going to miss greens, I'm going to miss greens on hard days, and if I can just grind myself out and make pars, it would be great. If I can hit a little bit better tomorrow, that would be fantastic."

McIlroy, playing his first British Open since his victory at Royal Liverpool in 2014, came out firing. He birdied three straight holes on the front nine, including the famed par-3 "Postage Stamp" at No. 8, to go to 4-under and tie for the lead. That changed with a shot over the green, a poor chip and three putts for a double bogey on the 13th, and he was so angry that he dropped another shot on the 14th.

"I think if I would've stepped on the first tee and someone would have given me a 69, I probably would have taken it," McIlroy said. "But if somebody had given me that score on the 10th, I probably would have."

The real test could be Friday with rain in the forecast. McIlroy, despite his roots in Northern Ireland, is not regarded as a player who thrives in bad weather. His hope is that the bad weather clears out by the time he tees off Friday afternoon.

"I don't think we're going to see the course like this for the rest of the week," he said.

The Associated Press contributed to this report.