NEW YORK — For quite a while, Novak Djokovic’s opponent in the U.S. Open semifinals, Gael Monfils, looked as if he didn’t want to win — or even be there at all.

That premeditated “great strategy” of hoping to lull the No. 1 seed and defending champion into complacency and mistakes, as Monfils described it later, worked briefly, yet did not prevent a two-set deficit. So he transformed back into his entertaining, athletic self. A sweat-soaked Djokovic sought help from a trainer for aches in both shoulders, and what was no contest suddenly became one.

Monfils forced a fourth set, and Djokovic ripped off his white shirt angrily a la “The Incredible Hulk.”

The ultimate outcome was only briefly in the balance, though. Djokovic regained the upper hand, as he so often does, reaching his 21st Grand Slam final and seventh at the U.S. Open with an eventful and, at times, bizarre 6-3, 6-2, 3-6, 6-2 victory over Monfils on Friday.

“Well, it was a strange match,” said Djokovic, who will face No. 3 Stan Wawrinka in Sunday’s final, “as it always is, I guess, when you play Gael, who is a very unpredictable player.”

Never more so than on this muggy afternoon, with the temperature at 90 degrees and the humidity above 50 percent. Monfils, now 0-13 against Djokovic, spent most of his news conference defending his unusual approach and said he knew beforehand he might try it.

On ESPN’s telecast, John McEnroe blasted the 10th-seeded Frenchman for lack of effort. The Arthur Ashe Stadium crowd jeered him.

“First question is, like, ‘You’re not competing?’ … Yes, I’m competing,” Monfils said, cursing for emphasis. “I made a sign to my coach (to) say, ‘OK, I’m going to Plan B.'”

Djokovic had three set points while serving at 5-1, 40-love, and Monfils transitioned into something that at first blush appeared to be “tanking” — losing on purpose, for who knows what reason — but which he explained afterward was the tennis equivalent of Muhammad Ali’s boxing “rope-a-dope,” absorbing someone else’s best shots and pretending to not be interested in attacking.

Instead of his usual crouch preparing to return serves, Monfils casually stood upright at the baseline, without a worry in the world, looking like someone waiting to place his takeout espresso order. During points, Monfils would hit slices or make halfhearted, half-swinging strokes, then occasionally wallop a 100 mph passing shot.

“For sure, people are not really ready to see that,” Monfils said. “Definitely, I try to get in his head, try to create something new for him to see.”

Somehow, the tactic was effective, for a short while, anyway.

“I was completely caught off-guard,” Djokovic acknowledged.

Miscue after miscue arrived from Djokovic, and Monfils won three games in a row, before eventually dropping a set for the first time all tournament.

“I thought, at times, that he was maybe behaving a little bit — for some terms and judgments — unacceptable,” Djokovic said. “But I guess that was part of his tactics. If he said that you have to believe him, I guess.”

Djokovic will try for his third U.S. Open championship and 13th major trophy overall against Wawrinka, whose first final at Flushing Meadows came via a 4-6, 7-5, 6-4, 6-2 victory over No. 6 Kei Nishikori that lasted more than 3 hours and finished with the roof shut. Djokovic has won 19 of 23 previous meetings, but Wawrinka did win their 2015 French Open final for his second Grand Slam title.

Wawrinka was down a set and a break against Nishikori, who eventually faded in the heat and mugginess. Wawrinka got so sweaty his racket flew out of his hand on one point, but he seemed to grow sturdier as the match wore on.

At the start, Wawrinka said, Nishikori “was always dictating. I was feeling uncomfortable on the court. He was coming at the net. … I just tried to, little by little, play a little bit better, a little bit faster, a little bit heavier. I tried to make him run.”

Wawrinka has spent nearly twice as long on court as Djokovic has so far: a little under 18 hours vs. a little under 9 hours.

That’s because Djokovic enjoyed the easiest path to a major semifinal in the nearly half-century of the Open era: Three of his first five foes pulled out of because of injuries. Then came this 2 1/2-hour miniseries, topping them all for oddness.

In the second set, Monfils lost five consecutive games, and limped afterward. Soon, Djokovic led 2-0 in the third, breaking on a double-fault that drew boos and whistles. All over but the shouting, right? Nope. In a blink, Monfils awoke.

Hours before the match, Djokovic clutched at his back during a practice session in Ashe. Behind 5-2 in the third, Djokovic got his left shoulder massaged. Later, it was time for help with the right shoulder. Asked what health worries he might have, Djokovic replied, “Thankfully, it’s behind me. So I don’t have any concerns.”

In the late going, Monfils was leaning on his racket between points. More examples of playing possum? Perhaps. But Djokovic showed his own signs of distress in the tough conditions.

After all of that, Djokovic plays Sunday for his third Grand Slam championship of 2016. He won the Australian Open in January, and the French Open in June — when the theatrics were at a relative minimum by Friday’s standards.


Follow Howard Fendrich on Twitter at http://twitter.com/HowardFendrich