Dustin Johnson acknowledges fans after he birdies the ninth hole...

Dustin Johnson acknowledges fans after he birdies the ninth hole during the final round of Northern Trust PGA tournament at Glen Oaks Club in Old Westbury on Sunday, Aug. 27, 2017. Credit: Kathleen Malone-Van Dyke

The golfer officially ranked No. 1 in the world squared off against the one generally considered the best in the sport right now. They went toe to toe. Fists were flying, too — as Dustin Johnson and Jordan Spieth each punched the air to mark every key moment in a Northern Trust tournament that went to a playoff and emerged as an instant classic.

After they had traded momentum swings and unlikely huge putts, Johnson won the trophy for the FedEx Cup playoff opener Sunday at Glen Oaks Club, a first-time host that proved to be a heavyweight in its own right.

Johnson had the final say, sinking an 18-foot twister on the final hole of regulation, then smoking a tee shot on the same hole in the playoff. That set up a wedge shot that landed 4 feet from the hole and a birdie that set off a roar from the gallery in Old Westbury.

“It was a lot of fun. It was fun to finally be in the hunt again and know that my game is going to hold up under the pressure,” the champion said after he overcame a five-stroke lead by Spieth, a three-time major champion, three-time winner on tour this season and leading contender for player of the year.

Spieth said, “I thought it was a fun show to be a part of. I was hoping it wasn’t going to be that much fun.”

Their back nine took on the feel of match play because the two had pulled away from the rest of the field on the challenging layout. It also had the intensity of a boxing match, with virtual haymakers being thrown, such as Spieth going ahead with a birdie on the par-4 14th hole and Johnson answering with one on the par-3 15th. Both hit into the right bunker on the par-3 17th. Spieth appeared certain to drop a shot but rammed home a long putt.

One hole later, Johnson chose to lay up out of the thick Glen Oaks rough and needed to make the difficult 18-footer, which started right of the hole and went in on the left side of the cup. “I wasn’t rooting for him to make it,” Spieth said to laughter at his news conference. “About three feet out, I thought it was high from my angle.”

Johnson, having experienced his share of heartache (including the 2015 U.S. Open against Spieth), said later, “I thought it was going to miss, for sure. But obviously it turned just enough.”

It all was quite an initiation for tournament golf at Glen Oaks. Attendance had been light and the atmosphere quiet earlier in the week. But on Sunday afternoon, it sounded like an Islanders-Rangers game, with roars for both sides.

“I love playing in New York,’’ Johnson said. “The fans like me, and so I hope they continue to like me because if they don’t, that’s not any fun, because they can be mean. I think the fans out here are great. I had a really good time this whole week.” On the 18th green, Johnson hugged and kissed his fiancé, Paulina Gretzky, whose famous father, Wayne, never won in overtime on Long Island in the playoffs.

The playoff was striking. Literally. Johnson chose not to repeat the safe route down the right side that had caused him trouble on 18 in regulation. Spieth said that the wind shifted between regulation and the extra hole, so it was behind the golfers the second time. Johnson said that as long as it wasn’t in his face, he was going to go all out: He would attempt to hit over a lake and a bunker.

“It’s only a 300 (yard) carry. I can cover that,” said the player who blasted the shot more than 330 yards. From there, it was game, set and match.

None of this had been imaginable three hours earlier, as Spieth had expanded his third-round lead of three strokes to five with birdies on the third and fifth holes. The Northern Trust was all but in his back pocket when he stepped to the tee on the par-3 sixth. But in a flashback to his soaked meltdown on the 12th hole at Augusta last year, he put his shot in the water and made double bogey.

“It’s very difficult holding a lead on a difficult golf course when the guy you’re playing with goes bogey-free and doesn’t really sniff a bogey and shoots 4 under. Hats off to DJ,” said the reigning British Open champion. “I didn’t lose the tournament. He won it.”

Johnson had appeared poised to win the Masters and much else in April, when he was coming off three victories. But he injured his back in a fall at his Augusta rental home, pulled out of the tournament and never has been the same — until he showed up in Old Westbury. “This is the first week that I felt my game was in really good shape and back to where it was,” he said.

He joked early in the week that he had no problem being a forgotten golfer despite his No. 1 place in the Official World Golf Ranking. Sunday night, he said, “I don’t forget myself.”

No one who was at Glen Oaks on Sunday soon will forget what they saw there, either.

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