Phil Mickelson must have walked off Royal St. George's and wondered what hit him.

The opening round Thursday in the British Open was accommodating enough for 47 players to post scores in the 60s, led by Louis Oosthuizen at 6-under 64.

Mickelson didn't break 80.

He failed to register a single birdie, took double bogey on the final hole and shot 80, his worst start in the 27 times he has played golf's oldest championship.

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The good news for Mickelson? He still ends the year as a major champion, having captured the PGA Championship two months ago at age 50.

Mickelson wasn't alone in failing to take advantage.

U.S. Open champion Jon Rahm, trying to become the first player since Tiger Woods in 2000 to win golf's two oldest majors in the same year, hit the face of a fairway bunker on the ninth hole and made a double bogey. Worse yet, he managed only two birdies for a 71.

Bryson DeChambeau couldn't find the fairway and never got any momentum until early in the back nine when he ran off enough birdies to at least salvage a 71.

Both of them played in the morning, before the links began to get drier and a little bouncier. The afternoon played just over 1 1/2 shots harder.

"If I can figure out how to make that driver go straight and figure out the jumpers out of the rough, it would be awesome," DeChambeau said. "I just can't figure it out."

Only five players have broken par over 72 holes at Royal St. George's the last two times it hosted the British Open. The course figures to get drier and tougher for the rest of the week, and the number of players in red figures — 47 — will start shrinking quickly.

But this was the day, morning or afternoon, to make hay.

Justin Thomas couldn't make a birdie. Thomas, who has such great control of the flight of his irons that he would seem to be a natural for links golf, scrambled out of ankle-deep grass for pars and reached 1 under with a birdie on the tough par-4 fourth hole.

He didn't make another birdie the rest of the way, dropped three shots and opened with a 72. That left him in a tie for 91st, along with Patrick Reed.

Rory McIlroy shot 70 and realized it could have been worse.

He began the Open with wedge to 3 feet for birdie. He drilled it down the middle of the next fairway — the ball winds up in the middle more than actually aiming it there — and stuck another wedge in tight. He missed that putt, however.

And then he ran off a string of three straight bogey and was still 2 over with five holes remaining. The frustration began to show, especially on the 17th hole. Another great tee shot, McIlroy had wedge in hand and sent the ball high and soaring to the right, some 50 feet beyond the pin. He had to scramble for par.

A birdie on the last hole gave him hope.

"The conditions got pretty rough there in the middle of the round. The wind got up and I made a few bogeys in a row," McIlroy said. "Sort of said to myself at the turn if I could get back to even par for the day I would be happy.

"To birdie the last hole and get back to even par, yeah, it’s nice to finish like that," he said. "Looking forward to getting back out there tomorrow."

It was more challenging in the afternoon, with sustained gusts and the turf starting to get dry. Even though, Webb Simpson was among those who managed a 66 in the afternoon. Former PGA champion Collin Morikawa, in his first test of links golf, had a 67.

Tommy Fleetwood also had a 67.

"First round of the Open, you can only lose it on the first day," Fleetwood said. "It's nice to have shot a good round and get going and move on to tomorrow."

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Rahm, Thomas, DeChambeau and anyone else who over par are certainly not out of the tournament. They just failed to take advantage of a day when good scores were available.

Mickelson is another story. He was tied for last place. Only twice in the last 20 years has a player shot 80 in the first round and even made the cut. The most recent was Paul Lawrie in 2013 at Muirfield. Ernie Els opened with an 80 at Royal Birkdale and went on to tie for seventh.

There's one difference, though. Els was among 19 players who shot in the 80s that day (it would have been 21 if Sandy Lyle and Rich Beem had walked in early). On this day, Mickelson shared that space with Deyen Lawson, a local qualifier.