SOUTHPORT, England - Jordan Spieth was playing against one of the world’s best golf courses, against his friend Matt Kuchar and no less significantly against himself. On one of the longest days in the 146-year history of British Open he was able triumph over all three.

Spieth, having tossed away the lead and seemingly the Open, burst out with an eagle and three birdies Sunday to go 5-under par the last five holes, win by three shots and at age 23 join the great Jack Nicklaus as the only golfer to win three majors before the age of 24, which he turns Thursday.

“I put a lot of pressure on myself, unfortunately,” said Spieth, “and not on purpose, before the round today, just thinking this is the best opportunity that I’ve had since the ’16 Masters. And it weren’t to go my way today, then all I’m being questioned about and thought and murmured about is in comparison to that.”

The 2016 Masters is when he blew five-shot lead the last nine holes, but Sunday after what at the start of the round had been a three-shot became a one-shot deficit, Spieth showed his courage and putting touch and came in a one-under 69 for a 12-under 268.

That was three shots ahead of Kuchar, who after some bizarre happenings — and a long wait — at 13, was ahead by one. Haotong Li, with the day’s best round, a 63, was third at 274. Rory McIlroy, who squandered his chances with a bogey at 15 — the hole Spieth would eagle — and Rafa Cabrera Bello tied for fourth at 275.

The 13th hole at Royal Birkdaleg is a 499-yard par-4 that plays through enormous sandhills. Spieth, at 8-under and with Kucher, his playing partner, drove right — far, far right — the BBC said 100 yards off line and unplayable.

He questioned officials about his options. “Is the driving range out of bounds?” he asked. “Where was my nearest point of relief?” The decision took maybe a half an hour, as Spieth went up and back and Kuchar knelt down.

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Spieth apologized to Kuchar for the delay, finally took a drop at the cost of a penalty, on the driving range where the equipment vans were parked. Then, on the advice of longtime caddie Michael Greller, hit a 3-wood, chipped on and one-putted for a bogey. For the first time Kucher was in front. But not for long.

Spieth, who said he felt less pressure as the man chasing not being chased, birdied the next hole, a par-3 200-yard 14th, hitting a 6-iron five feet from the cup, then was on the green of the 542-yard, par-5 15th in two and holed a 40-foot putt for a 3.

“I felt once I lost the lead completely and we were tied, I actually felt the nerves go away until I got the lead again,” said Spieth. “Then they were back.

“You just don’t know what your mind is going to do sometimes.”

This from someone who in 2015 as Jack Nicklaus and Arnold Palmer did in earlier years, won the Masters and U.S. Open. That 2016 Masters, however, when he hit two balls into the creek at 12, shook him and made doubters of some others.

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When the situation Sunday got shaky, Greller reminded Spieth a few days earlier he had been with Michel Jordan, Michael Phelps and other top athletes. “You belong in that group,” the caddie reassured him.

Spieth proceeded to prove his caddie right.