Johnson had four birdies on the front nine then birdied three of his final five holes to reach nine-under 201 at TPC Harding Park in San Francisco.
It was the eighth straight round in the 60s at the PGA Championship for Johnson, who nearly chased down Brooks Koepka in the final round at Bethpage Black last year before losing by two shots.
“I putted really well,” said Johnson, who shot 31 on the back nine. “That was key. But I hit a lot of good shots to give myself some good looks because the flags are tucked. The greens are firm and fast. So I did hit a lot of quality iron shots.”
Americans Scottie Scheffler (65) and Cameron Champ (67) were tied for second at eight-under 202.
Two-time defending champion Koepka shot a one-under 69 and was tied for fourth with American Collin Morikawa and England’s Paul Casey on 203.
Frittelli, meanwhile, was the top SA player heading into the final round. He was in a tie for 21st place at three under.
Koepka, who is trying to become the first since the 1950s to win the same major three years in a row, looked unflappable until a bogey on the 13th hole began his back nine struggles.
A stretch of three straight bogeys moved Koepka down the leaderboard but he recovered quickly with birdies on 16 and 18.
Johnson roared home Saturday, making birdie putts of 26 feet on the par-4 15th and 20 feet on the par-3 17th.
He began his round with a par but then drained a 17-foot birdie putt on the par-4 second.
Johnson made back-to-back birdies on the fourth and fifth holes before running in trouble on six, but even that bogey and a double bogey on the par-4 ninth couldn’t put a damper on his brilliant round.
“The golf course is tough. Obviously a bogey would have been a lot nicer, but I knew I was playing good,” he said of the ninth hole. “I was putting good. I just needed to keep on going and put it behind me.”
– DJ’s best birdie day –
His eight birdies are the most he has made in any round at a major, bettering the seven birdies he made at the 2017 PGA Championship and the 2014 British Open.
Earlier this year, Johnson extended his season victory win streak to 13 years by capturing the Travelers Championship. That also halted a 15-month victory drought.
His results have been mixed in 2020 as he missed the cut at the Memorial, withdrew from the 3M Open with a bad back after an opening 78 and finished 12th at the WGC event in Memphis.
Koepka was cruising until he got to the most treacherous part of the course, the par-4 13th, where he made bogey. His three-hole wobble began with his first bogey of the round.
His shot from the edge of the green went well past the hole and he had to make a seven-foot putt for bogey. He then bogeyed 14 and 15.
On 15, he landed in a deep rough off the green and his chip fell well short, giving him another tough chip shot to get on the green.
It could have derailed Koepka’s chances but the American came right back with a four-foot birdie putt on 16,and, after a par on 17, closed with a six-foot birdie putt.
“I thought I played a lot better than my score reflected,” Koepka said. “I felt like I played really well, putted really well, and the driver I hit great.”
Third-round leader Li Haotong of China shot a 73 and, like Koepka, struggled on the par-4 13th, making a double bogey.
But Li, trying to become the first player from China to win a major, never recovered from that and made two more bogeys before 18 and finished on 205.
Tiger Woods saw his chances all but extinguished as he struggled on the greens for the second straight day and shot a 72.
The 15-time major winner and reigning Masters champion is tied for 59th at 212, 11 behind Johnson.
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