AP

SOUTHPORT, England (AP) — Jason Day thought there might be a 62 out on the course as he played a suddenly vulnerable Royal Birkdale on Saturday, a few groups ahead of Branden Grace.

Actually, he thought he could have easily shot one himself.

"I think I left four in the heart today that would have got me to 9 (under) if I holed those," Day said after shooting a 5-under-65. "So I definitely think there's a good opportunity to shoot 62 out there today."

Less than an hour later, Grace two-putted from behind the green on 18 to post his 62. The South African didn't know it at the time, but it was the lowest score ever shot in a major championship.

It came as no shock to Day or anyone else. The first player out on the course shot a 65 and his marker — who works in the pro shop at Royal Birkdale — nearly broke par himself.

By the end of the day 15 players had shot 66 or better. Leader Jordan Spieth at 11 under was six shots lower after three rounds than anyone in the nine previous Opens held here.

Never had Royal Birkdale looked so beautiful, all green and bathed in sunshine. Never had it been so vulnerable to an assault by the world's best players.

One day they were just trying to survive in the rain and wind. The next they were feasting on a golf course that looked like it belonged in the January rotation in Palm Springs.

"There was talk that 62 could be on," said Paul Casey, an Englishman who is quite familiar with the vagaries of his country's weather.

No tournament is affected more by the weather than the British Open. It can mean the difference between breaking par, as many struggled to do on Friday, and breaking records like Grace did in the third round.

It's been that way for 145 Opens before this, and it's certainly ringing true this week.

Where else could Dustin Johnson be — even if it was ever so slightly — disappointed in a 64?

"It was good," Johnson said. "But the conditions are pretty benign out there, with the greens being soft, the course is soft. You hit good shots, you get rewarded."

If this was the U.S. Open there would be plenty of hand wringing and consternation. The idea in that tournament is to test players so much that they will run around high-fiving fans if they ever get under par.

It doesn't always work, as judged by the low numbers at Erin Hills last month. Justin Thomas shot a 63 in the third round of that Open, and that was on a par-72 golf course.

The difference at the British Open is that the R&A doesn't really care what players shoot. The lowest one at the end of play on Sunday will end up with the claret jug regardless.

Right now, Spieth is the odds-on favorite to be that player. Incredibly for a major championship, he has shot two rounds of 65 that were both bogey free.

And on Saturday, he and Kuchar combined for 12 birdies playing in what is usually a place of tension in the final group. There were so many birdies that a couple of times the two were confused about who had the honor on the next tee.

"You could not have had better conditions with weather, with temperature, with rain overnight," Kuchar said. "It was very scoreable. I don't think there are many days that Royal Birkdale sees that are quite like this."

Spieth had that figured out long before he got to the golf course, as he watched on TV from home as players had their way with the golf course early.

Asked what he took out of his viewing, Spieth said "That Royal Birkdale notoriously difficult had just become one of the easier golf courses that we play for one round for the year."

That could change Sunday, which is the beauty of this tournament. A mixture of rain and clouds is forecast, and after the last few days of changing weather it's anyone's guess.

But while Mother Nature can be fickle, there's little man can do at this time to change the course. The greens are fairly slow and rolling perfectly, the rough isn't terrible, and balls that might in firmer conditions find their way into fairway bunkers are staying put.

The one constant in the British Open isn't what the score will be, anyway.

It's that the player who best manages the course — and the weather — will find a way to win.