Roger Federer in peak form, according to rival Novak Djokovic

NEW YORK -- Novak Djokovic is the top seed for the US Open, which begins Monday, but he believes that No. 2 seed Roger Federer may be playing the best tennis on the men's side of the draw.

"He's playing some of the best tennis of his life," Djokovic said Saturday during Arthur Ashe Kids' Day at the USTA Billie Jean King National Tennis Center. "Many people did talk about his career coming to an end after that season [2013] that was below his standard, but he came back stronger."

Federer, 34, hasn't won a Grand Slam title since July 2012, but Djokovic said Federer's style is giving him an advantage.

Among other things, Djokovic said, Federer's new emphasis on attacking, offensive tennis is so unusual in this era of long-range baseline dueling that it has thrown his rivals in the Big Four off-balance.

"He's using every possible opportunity to come to net. He makes things happen very fast," Djokovic said. "[Andy] Murray, [Rafael] Nadal, myself ... we like a little more time. I think he knows that. Tactically, he's trying to take time away, and he's very fit as well."

Federer avenged his loss to Djokovic in this year's Wimbledon final with a win in the last big US Open tuneup in Cincinnati last weekend. Federer also defeated Murray at that event.

But if Federer has a nemesis, it is the fourth member of the Big Four, Nadal.

Nadal is down to No. 8, and his seeding has him positioned to play Djokovic in the quarterfinals. Nadal would meet Federer, against whom he is 23-10, in the final.

But Nadal has struggled -- sometimes mightily -- throughout the year. He won the US Open in 2013 but was unable to defend his title because of a wrist injury. He is flying under the radar, but his record at the US Open since 2010 is 20-1, with two titles.

"Nadal has been down, and he's come back to win here before," Djokovic said.

Nadal was unusually forceful in making a case for himself. He said he feels sure that he would return to his "high level" again and added that he is close to that point. Asked how he feels about being described as an underdog, Nadal's reply was almost cryptic.

"We'll see who the favorite is in a couple of weeks," Nadal said. "That's the real thing. There are some players who are arriving with more victories than me this year, but I'm going day by day."

While Nadal has a tough first-round match against 18-year-old Borna Coric, Murray is involved in the most sensational matchup. He will face 20-year-old Nick Kyrgios, who created a controversy with his comments toward Stan Wawrinka during the Rogers Cup in Montreal.

"He's using every possible opportunity to come to net. He makes things happen very fast." Novak Djokovic, on Roger Federer's challenging style

Many people aren't willing to cut Kyrgios much slack in the wake of that incident. Murray is not one of them.

"Nick's a young guy, and we all make mistakes," Murray said. "... I think it's wrong, a lot of the things that he's done, but I just think a little bit of patience is important when it comes to Nick because he's a young guy and it isn't easy growing up in the spotlight."

Murray has played well against Kyrgios, beating him in all three meetings, two of them at Grand Slam events, without losing a set. But Murray uses the same word as everyone else when talking about the mercurial Aussie: "unpredictable." The 6-foot-4 Kyrgios is rangy, with an outsized game capable of blowing even a great defender like Murray off the court.

And Murray knows Kyrgios enjoys the limelight.

"He likes playing on big stages," Murray said. "Last year, he won only one or two matches outside of Slams the whole year. This year, his results have been inconsistent, but at the Slams he made quarters in Australia, third round at the French, fourth round at Wimbledon. I would expect him to be ready for the match. He gets all fired up for the big events."

Murray, seeded No. 3, is in third quarter of the draw, Federer in the fourth. They could meet in the semifinals -- just like at Wimbledon. Federer handled Murray with ease there, but that may not be what stands out most prominently in Federer's mind about that match.

"Looking back at Wimbledon now, maybe I peaked too early against Murray," Federer said. "After that, I didn't quite play just as good against Djokovic."

Federer would be more than happy to get the chance to test his theory, but Nadal's approach is the most prudent: You take it day by day.