NEW YORK — For quite a while, Novak Djokovic's opponent in the U.S. Open semifinals, Gael Monfils, played as if he didn't even want to be there. That "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 Monfils transformed back into his entertaining, athletic self. A sweat-soaked Djokovic sought help from a trainer for aches in both shoulders, and what had been 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 and reached 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 Friday. "Well, it was a strange match," said Djokovic, in the understatement of the tournament, "as it always is, I guess, when you play Gael, who is a very unpredictable player." Sunday, Djokovic will try for his third U.S. Open title, and third major title of the year and 13th overall, facing No. 3 Stan Wawrinka, who beat No. 6 Kei Nishikori 4-6, 7-5, 6-4, 6-2 to make his first U.S. Open final.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. "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, 'Okay, I'm going to Plan B.' " Djokovic raced to a 5-0 first-set lead and earned a set point after all of 19 minutes, but Monfils held there. With Djokovic in possession of three more set points while serving at 5-1, 40-love, Monfils transitioned into something that might have appeared to be an attempt to lose on purpose 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 not to be interested in attacking. Monfils casually stood upright at the baseline. During points, he hit slices or made halfhearted, half-swinging strokes, then occasionally walloped a 100 mph passing shot. Monfils even repeatedly tried to serve and volley, a style he almost never employs, and erred often. "Definitely, I try to get in (Djokovic's) head, try to create something new for him to see," Monfils said.Somehow, the tactic was effective for a bit. Djokovic started making miscue after miscue, and Monfils won three games in a row before dropping a set for the first time all tournament. "I was completely caught offguard," Djokovic said. Prodded by reporters about what he thought of the way Monfils played, Djokovic said, "I thought, at times, that he was maybe behaving a little bit — for some terms and judgments — unacceptable. But I guess that was part of his tactics. If he said that, you have to believe him, I guess." In the second set, Monfils lost five games in a row and 20 of 24 points in one stretch, and came up limping afterward. Soon enough, Djokovic went up 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 came to life. When he broke back to get to 2-all, he raised his right fist and the fans roared, now backing him. Monfils won five consecutive games, including one spectacular point in which he took a long run to get to a short ball, then reversed direction for a leaping volley winner. Hours before the match, Djokovic had clutched at his back during practice. Behind 5-2 in the third against Monfils, he got his left shoulder massaged. Later, he got help with the right shoulder during a medical timeout. By the end, he was hitting second serves in the low 80s mph or below.These would constitute new trouble spots for the Serb, who arrived in New York with concerns about his left wrist, then got treatment on his right elbow during his first- and fourth-round matches. Asked what worries he might have about his health, Djokovic replied, "Thankfully, it's behind me. So I don't have any concerns."