Rafael Nadal's impressive return from a seven-month injury layoff, with a haul of nine titles including a French Open and an unbeaten 15-match hardcourt run, has made him a marked man at the US Open.
"Nadal is definitely back and he's playing maybe the best tennis that he ever has played on hard courts," said world No.1 Novak Djokovic.
"He's definitely so far the best player this year. There is no question about it. The results are showing everything."
After healing the nagging knee injuries that have bothered him for years, Nadal dominated on his beloved clay with wins in Sao Paulo, Acapulco, Madrid, Rome, Barcelona and Roland Garros for his 12th career grand slam crown and eighth French Open title in nine years.
But what impresses his rivals on the Flushing Meadows hardcourts, where the year's final grand slam event starts on Monday, is his unbeaten run on hard courts, taking titles in Indian Wells in March and in August in Montreal and Cincinnati in his US Open tune-ups.
"He has beaten some tough players in tough tournaments," defending US Open champion Andy Murray said.
"It's not like he's had easy draws or whatever. He's beaten some top, top players. Yeah, he's going to be very difficult to beat here."
Nadal, for his part, plays down the performance.
"I had a great summer, but that's all. Doesn't mean nothing else," he said. "I hope to be very competitive for the first match."
Djokovic sees a more attacking Nadal adapting to the hardcourts to help ease the stress on his knees.
"He seems like he changed a little bit," Djokovic said. "He stepped in a little bit more. He knows that now he has to be a bit more aggressive than he usually is because of, I guess, his knees and everything and because hard court is not clay. It's not his favourite surface. It's faster.
"I'm sure he worked on that and you could see that all the work he put in is getting results."
And 17-time grand slam champion Roger Federer, who could face Nadal for the first time at a US Open in the quarter-finals, has been dazzled by Nadal's performance.
"I'm very impressed, especially seeing him play really well on the quicker hard courts," Federer said. "He is someone to be reckoned with.
"He has had an incredible season so far."
Nadal, Murray and Djokovic are each seeking a second slam title this season and a leg up in year-end world No.1 honours.
"If I am No.1, it will be amazing, amazing season for me," Nadal said. "If I am not No.1, it still will be amazing season for me. This tournament is going to make a big difference."
