Hot Nadal, balky knee hit US Open

NEW YORK — Ask Rafael Nadal how his famously troublesome left knee is feeling on the eve of the U.S. Open, and he'll balk a bit while formulating a response.

"I am ..." the 12-time major title winner began, haltingly. "You know ..." he resumed, before smiling sheepishly and pausing again.

Eventually, Nadal offered something of a complicated answer.

"I have to say that I am very well, because the results have been amazing since I came back," he said. "If I say something else, (it) will sound strange."

That's because when the year's last Grand Slam tournament begins Monday, none of the players setting foot on the blue hard courts of Flushing Meadows possesses as much momentum — or is in as fine form — as the No. 2-seeded Nadal. He's won his past 10 matches heading into the first round against 97th-ranked Ryan Harrison of the United States.

The biggest curiosity when it comes to Nadal these days is how his knees will hold up. They've presented recurring problems for him over the years, particularly the left one, which kept him out of action from late June 2012 until February 2013. He missed the London Olympics, last year's U.S. Open and this year's Australian Open.

"I feel more comfortable now than six months ago, that's for sure," Nadal said, then quickly added: "But I still have pain some days."

Hard courts could exacerbate the matter because of the pounding legs take on the unforgiving surface. Yet Nadal is 15-0 on hard courts in 2013, with his current run of victories built en route to titles at Montreal and Cincinnati.

"He's on a great streak right now. He's playing fantastic tennis. He's playing as well as anyone in the world right now," said Harrison.