NEW YORK -- While Rafael Nadal was improving to 19-0 on hard courts in 2013 by returning to the U.S. Open quarterfinals, he noticed the scoreboard updates showing how Roger Federer's match on another court was going.
So Nadal knew right away that he would not play Federer next.
"When you are in the changeovers, you see what's going on," Nadal said. "But I don't (pay) attention. I just saw, and that's it."
The second-seeded Nadal, who counts the 2010 U.S. Open among his 12 Grand Slam titles, came back to beat 22nd-seeded Philipp Kohlschreiber of Germany 6-7 (4), 6-4, 6-3, 6-1 on Monday night in the fourth round.
Their match ended about 2½ hours after Federer was upset in straight sets by 19th-seeded Tommy Robredo, Nadal's quarterfinal opponent. Had Federer won, he and Nadal would have played each other for the 32nd time -- and first at Flushing Meadows.
In an interview the day before the tournament began, Nadal spoke about how he and Federer "deserved a final here," the way they met in four title matches at the French Open, three at Wimbledon, and one at the Australian Open. Nadal won six of those eight, part of his overall 21-10 head-to-head edge.
"Didn't happen. (That doesn't) mean cannot happen in the future. We'll see. Hopefully," Nadal said. "But is true that we are getting older, so the chances are less today than five years ago."
Federer is 32, Nadal 27.
And while Federer's skills are clearly in decline, Nadal is playing about as well as ever.
He's certainly excelling on the sort of hard courts used at the U.S. Open. This is his fourth tournament on the surface this season, and Nadal won the title at each of the first three.
Through four matches in New York, Nadal has not lost a single service game. That's 56 consecutive holds.
Against Kohlschreiber, he faced only one break point, in the opening game of the fourth set. But Kohlschreiber threw away that chance by badly missing what should have been a routine overhead, drilling the ball directly into the net.
"I was very lucky that Philipp had a big mistake with his smash," Nadal said. "That's why I didn't lose my serve."
He also pointed out that it's not so much his serve itself that is the key to the success he's having -- "My serve is working just amazing," Nadal said sarcastically, smiling widely -- but instead, what matters is the way he is hitting the ball from the baseline once points are under way.
Indeed, Nadal was not particularly pleased with the way he served in the early going Monday.
"Four matches without losing ... serve is great. I don't want to lie. Happy for that. But I felt at the beginning today, I didn't serve my best," he said. "In the next sets, I am very happy the way that I served. I was able to win a lot of points and ... start a lot of points in a good position."