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Novak Djokovic celebrates his five-set semifinal victory over Roger Federer. ((Matthew Stockman/Getty Images))

Facing two match points against a beloved player whose name is already in the history books, Novak Djokovic clenched his jaw and flashed an ever-so-slight glimpse of a smile.

"I would lie if I say I didn't think I'm going to lose," Djokovic said.

Might as well go down swinging, right?

He turned violently on a 108 mile-per-hour serve from Roger Federer for a cross-court winner that barely nicked the line. The fans in New York's Arthur Ashe Stadium, ready to explode for a Federer victory, instead found themselves taking a cue from Djokovic — who raised his hands, asking for a little love.

About 10 minutes later, those same fans were dancing with Djoko as he boogied at centre court to celebrate an epic U.S. Open semifinal win — one in which he dug out of a two-set hole, then saved two match points against Federer for the second straight year.

Top-seeded Djokovic won 6-7 (7), 4-6, 6-3, 6-2, 7-5 Saturday to improve to 63-2 on the year. This was only his second career comeback from two sets down, while Federer lost a two-set lead for the second time in three months after going 178-0 lifetime before this year's Wimbledon quarter-finals.

Next, Djokovic will face defending champion Rafael Nadal on Monday in a rematch of last year's final. No. 2 Nadal beat No. 4 Andy Murray 6-4, 6-2, 3-6, 6-2 in the later semifinal. Djokovic is 5-0 against Nadal this year. All the meetings have been in tournament finals, including Wimbledon.

"I didn't find the solution yet. I will try my best," Nadal said. "I play last year's final against him. I think I played a fantastic match. I will try the same."

Nadal's four-set win over Djokovic last year made him the fourth man to win three Grand Slam titles in a year since the start of the Open era. Djokovic could become the fifth, though he said regardless of what happens, the comeback win over Federer will always stand out.

"It was definitely the biggest win of this year, one of the biggest wins of the career under the circumstances," Djokovic said. "Roger was in control, playing better. I switched gears and played much better over three sets."

So much better, in fact, that after the fourth set, the prospect of third-seeded Federer ever getting a match point seemed bleak.

Djokovic, who spent the first two sets shaking his head, commiserating with the folks in his players box, even folding his hands in mock prayer, turned things around suddenly and unexpectedly.

He got 16 of 20 of his first serves in during the fourth set and ripped off the first 15 service points. But Federer won the next three of those service points, all with the set on the line, to show an inkling of resistance — and give a preview of a fifth set that had as many momentum shifts as the match.

The real action began with Djokovic serving at 3-4 and stringing together an uncharacteristically bad game, getting broken at love on two mishit forehands, a framer of Federer's that set up a winner and a double fault after a second serve that missed the line by about a foot.

After missing a backhand to open his service game at 5-3, Federer hit three straight serves Djokovic couldn't get back. He had two match points, same way he did last year in the semifinals, and the fans were squarely on his side, as he stood oh-so-close to making his 24th Grand Slam final and moving a win away to adding to his record 16 Grand Slam titles.

But Djokovic isn't putting together one of the greatest seasons in tennis history for nothing.

He knows all about risk-reward shots and figured being down two match points was as good a time as any to try it. Federer spun a serve wide to Djokovic's forehand side and the Serb took the all-or-nothing route.

"If it comes in, it comes in," he said. "It's a risk. Last year, I was in a very similar situation. He was two match points up. I was hitting a forehand as hard as I can. You're gambling. If it's out, you lose. If it's in, maybe you have a chance. I got lucky today."

Federer's next serve hit the back of the service line and jammed Djokovic, but somehow he got it back. Federer moved in and cranked a forehand, but it ticked the net and went out. Federer sprayed a forehand wide at deuce and suddenly, a crowd gearing for a Federer win was shouting "No-vak, No-vak, No-vak!"

They know a winner when they see one.

Counting the two match points he saved, Djokovic won 17 of the final 21 points.

Federer was among the 23,000-plus on a 27-C day in the stadium who couldn't believe how the last comeback began. He said Djokovic is the best version of the kind of players he faced as a kid — who start taking huge chances when they feel they have nothing else to lose.

"Then to lose against someone like that, it's very disappointing, because you feel like he was mentally out of it already," Federer said. "Just gets the lucky shot at the end, and off you go."

Thanks to the rain that scrubbed two days of play from this tournament, Djokovic will get a day's rest between the semifinal and the final, a break from the long U.S. Open tradition of closing things out on back-to-back days on the weekend.

Waiting for the men's semifinals to finish were Serena Williams and Caroline Wozniacki, who were scheduled for the women's semifinal in Ashe. In the other semifinal, No. 9 Sam Stosur defeated Angelique Kerber 6-3, 2-6, 6-2 on the Grandstand Court.

Djokovic avenged one of his only two losses this season. He fell to Federer in the French Open to snap a string of 43 straight victories — the third-longest win streak in the Open era.

Federer, meanwhile, was trying to win at least one Grand Slam tournament for the ninth straight season and appeared more than ready to grab this one.

Shortly after closing out a 9-7 first-set tiebreaker by hitting a massive, unreturnable backhand into the corner, Federer broke Djokovic twice in the second and was practically bouncing from point to point while Djokovic slumped his shoulders.

Djokovic began his rally by serving out the first game of the third set at love, then breaking Federer after five deuces.

He turned into a steamroller over the next hour and there was no avoiding the sense that a shift of power was being completed — from Federer, who won three Grand Slam tournaments in 2004, 2006 and 2007, to Djokovic, who was trying to do it this year, with Nadal also in the mix after accomplishing the three-fer in a 2010 season capped with a win over Djokovic in the final at Flushing Meadows.

But even with the loss, Federer showed he's not done.

To move within a point of the match after the way Djokovic played was a testament to what the 30-year-old still has left in the tank.

"I did all the right things in so many tournaments," Federer said. "But like I said, sometimes in sports it just goes the other way. Maybe you've already won so much that it evens it out a bit sometimes. I don't know."

2011 U.S. Open