Ten years ago, Phil Mickelson nearly won the British Open at Royal St. George’s, finishing runner-up to winner Darren Clarke.

After Thursday’s opening round at the same course, Mickelson is tied for last place after shooting a shocking 10-over-par 80, which placed him 16 shots out of the lead, and left him with no realistic chance at making the cut to play the weekend.

“I didn’t see that coming,’’ Mickelson said to his coach, Andrew Getson, as he left the scoring area, according to ESPN.com.

All Mickelson would say further to reporters was: “I’m in last place. I’ll try to do better tomorrow.’’

It was the second-highest score Mickelson has ever posted in 93 rounds played at the Open. Mickelson shot 85 during the third round in 1998.

Mickelson, 51, won the PGA Championship at age 50 to add a sixth career major championship to his brilliant résumé, but his form hasn’t been close to the same since his magical week at Kiawah Island.

Mickelson missed the cut at the Charles Schwab Challenge the week after the PGA, then tied for 62nd at the U.S. Open, tied for 61st at the Travelers Championship and tied for 74th at the Rocket Mortgage Classic in the lead-up to this week.

His round on Thursday never got going. He hit just 6 of 14 fairways, 9 of 18 greens and took 35 putts. He shot a 40 on the front nine with five bogeys and 40 on the back with four bogeys and a double on 18. He didn’t card a single birdie.

Entering the week, Mickelson conceded that he had no idea what to expect of his play.

“Your guess is as good as mine,” Mickelson said before Thursday’s round of his chances this week. “All I can tell you is that I like the course. So, as always, I’m looking forward to playing over here.”

Shane Lowry, the last man to win the British Open, winning at Royal Portrush in 2019 before last year’s Open was canceled by COVID-19, struggled to a 1-over-par 71 and called his form on Thursday “pretty average.”

His score notwithstanding, though, Lowry called it “very special day’’ for himself being announced as the reigning Open champion on the first tee.

“The announcement on the first tee, I’ve been waiting over a year for that, so it’s quite nice,” he said. “It was quite unsettling at the start. I got off to a pretty nervy start. I didn’t play my best golf. I battled hard. I was quite proud of myself. On to tomorrow.”

Louis Oosthuizen said on Thursday that he seems to have settled on a Ping putter that he feels comfortable with, hopefully for the long term. Why is this relevant? Because, by his own admission, Oosthuizen has been a player who goes through putters like writers go through notebooks.

“I’ve got a bag [of putters] at home that I might just throw in a river someday,” Oosthuizen said. “I went through a stage where I changed a lot of putters. Every week we were trying something. I realized quickly that there’s no way to find any consistency in putting if you do that.”

Richard Bland, the 48-year-old Englishman who recently ended a 477-tournament winless drought to win is first European Tour victory and get into the Open field, struck the opening tee shot Thursday morning and called it “very special, very nerve-racking.”

“I was OK when I got onto the tee,” Bland said. “A little bit nervous because you’re just about to start a major championship, but then once the announcer said, ‘It’s 30 seconds guys,’ you’re like, ‘Right, this is it. This is what it’s all about.’

“The nerves definitely sort of cranked up a little bit and was glad to get one down the fairway.”

Bland shot an even-par 70, but he’ll remember the day for the start.

“It was a tremendous honor, great for the R&A to put that on me,” he said. “It’s something that I wasn’t expecting at all. It was a special moment.”

Brian Harman, who’s one shot out of the lead after shooting a 5-under-par 65, missed the cut in his previous four Opens and was 16-over par in those eight rounds. … Since 1960, 73 percent of the Open champions have been inside the top 10 after the opening round.

… Will Zalatoris carded the first eagle of the tournament when he holed out from the fairway on No. 12 to get to 3-under. … Brooks Koepka shot 69, his 40th round in the 60s in majors since 2016 — eight more than any other player in that span. … When Jon Rahm double bogeyed the ninth hole, that snapped a streak of 102 consecutive holes without a double or worse.