Bubba Watson leads at Riviera, with Dustin Johnson (64) coming on strong

The second-round leaders spent most of Saturday’s third round treading water in the Genesis Open at Riviera Country Club. Occasionally diving a little deeper under par, never drifting far from the top of the leaderboard.

Then Dustin Johnson channeled his inner Michael Phelps, furiously stroking his way toward the front of the pack, and astonishingly, set himself up to make a run at successfully defending his title when the final lap is held Sunday.

Johnson, the No. 1 golfer in the world for a reason, finished with the best round of the tournament so far, a seven-under-par 64 that put him four strokes behind leader Bubba Watson and tied for eighth place. He started the day tied for 53rd, far enough behind that he was relegated to start the third round on the 10th hole.

He shot a six-under 29 on his second nine.

As is his custom, Johnson had a simple explanation for Saturday’s charge: “I think I just did everything very well.”

He had company in that regard. Several others also moved up the leaderboard into contention.

Watson, who won this tournament in 2014 and 2016, shot a 65 that included a tap-in eagle on the first hole and a five-under 30 on the front. He was three strokes behind leaders Patrick Cantlay and Graeme McDowell at the start of the third round.

Cantlay, thanks in part to a 54-foot birdie putt on the 18th hole, shot his second consecutive 69 and stands one back at nine under.

Cantlay, the former UCLA player who has not missed a cut in 18 tournaments since he came back from a back injury that cost him almost three seasons, dropped a stroke to par on the front, but played the second nine in three under.

“I played really well on the back,” he said. “On the front, I was close on a couple shots that turned out really, really bad. I just grinded through it and really made sure I was present for every shot. I felt like that paid dividends on the back side.”

McDowell (70) joined three other players tied for third, two strokes off the lead. Cameron Smith, with his second consecutive bogey-free round, matched Watson’s 65 and jumped up from 15th; Kevin Na shot 67 despite a double bogey on the par-four 12th, and Tony Finau, two shots off the lead to start the round, stayed there with a 67.

Watson got out to a quick start on the par-five first, set up by a 203-yard seven-iron to 1 1/2 feet.

“It calms you down real fast when you tap in for eagle,” he said.

Watson hasn’t won since his victory at Riviera in 2016. Last year, after losing a significant amount of weight in an over-rigorous dieting program, he had only four top-10 finishes in 22 starts, one of his worst seasons on tour.

He has regained some weight and is working his way back now.

“The trend is going in the right direction,” he said. “If I don’t win tomorrow or if I do win tomorrow, I’m still going in the right direction.”

Dustin Johnson plays his approach shot on the 12th hole during the third round of the Genesis Open on Saturday.

(Warren Little / Getty Images )

The round brought Johnson back from the deep end. He barely made the cut and stood at one over after 36 holes. He was one under at the turn Saturday.

“I was focused today,” Johnson said. “I knew making the turn, I looked over at AJ [his brother and caddie, Austin] and I said, ‘We’ve got 27 holes to see how good we are. We can get back in this thing if we play really well.”

Johnson eagled the first hole, added birdies on three, four, six and seven, and narrowly missed another on the ninth when his 16-foot putt slid just past the right edge.

The leaderboard, as it has been all week, is tight, with 14 players within five shots of Watson. Justin Thomas, whose 67 left him tied with Johnson, believes the first-place prize money of almost $1.3 million and 500 FedEx Cup points that go to the winner are up for grabs.

Asked how far behind the leader would be too far to make up the difference, he said, “I don’t think there’s a number here. In reality, I would say something like nine or 10, because if you’re playing well, you can shoot eight or nine under.

“It’s definitely a course that you can make a huge move up the leaderboard.”