By STEVE DOUGLAS

AP Sports Writer

SANDWICH, England (AP) — Even with his swing getting loose over the final hour Saturday, Louis Oosthuizen walked off the 18th green with a one-stroke lead at the British Open and another shot at ending his 11-year wait for a second major title.

A third round as undulating as the fairways at Royal St. George’s ended how it started, with Oosthuizen holding off Collin Morikawa and Jordan Spieth, and three shots separating them.

Oosthuizen, a runner-up in the last two majors, overcame his first real wobble of the tournament on the back nine with a key par save on the 15th and an 8-foot birdie on the par-3 16th that led to a 1-under 69.

That put him at 12-under 198 as the South African stayed on course to be the first wire-to-wire winner at golf’s oldest championship since Rory McIlroy in 2014.

Morikawa slid a 15-foot birdie putt just past the hole on the 18th green, settling for a 68 as he bids for a second major to go with his win at last year’s PGA Championship. The American was four shots behind after 10 holes and made a strong push at about the time Oosthuizen showed signs of fading. He trimmed Oosthuizen’s lead to one shot.

Spieth was tied for the lead until he bogeyed his last two holes — he missed a par putt from 2 feet at the 18th — to complete a disappointing back nine of lost chances. The three-time major champion had a 69 and was three shots back, just as he started the day.

It had all looked so different with an hour left in the day, with the three players tied for the lead at 11 under with four holes to play on a day the pin positions — not the weather — proved to be the greatest defense at Royal St. George’s.

The wind didn’t get above 10 mph and a cloudless sky with bright sunshine looked sure to bring another day of low scoring.

However, pins were tucked away, sometimes near slopes, while the firmer fairways brought the deep rough and pot bunkers into play.

It ensured some big names were unable to launch a challenge.

Top-ranked Dustin Johnson started four shots off the lead but plunged out of contention by making five bogeys in his opening 11 holes. Two late birdies could give him only a 73, leaving him eight shots behind.

Brooks Koepka, a four-time major champion, was a shot further back after managing only a round of 72.

McIlroy started much further back but reached the turn at 4 under for the championship after making five birdies. The back nine was another story and McIlroy threw an iron to the ground — he called it a “little toss” — during a run of three bogeys in five holes on his way to shooting 69, his first round in the 60s at Royal St. George’s.

It left him only on 1 under and with no chance of a second claret jug.

Instead, Corey Conners (66) and Scottie Scheffler (69) moved into contention at 8 under while Jon Rahm — looking to add the British Open to his U.S. Open from last month — shot 68 and was 7 under alongside MacKenzie Hughes and Dylan Frittelli.

Marcel Siem, who qualified from the second-tier Challenge Tour in Europe only last week, rebounded from an 8 after going out-of-bounds at the par-5 14th with two birdies in his final three holes. He was in a three-way tie for ninth place, six off the lead.

All of them are chasing Oosthuizen, who won at St. Andrews in 2010 and has rung up a career Grand Slam of runner-up finishes since then. That includes the U.S. Open last month, where he was leading with two holes to play until Rahm’s birdie-birdie finish. He also was runner-up in the PGA Championship to Phil Mickelson.

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Steve Douglas is at https://twitter.com/sdouglas80