NEW YORK --- When Rafael Nadal double-faulted on a break point Monday at the U.S. Open, it allowed Sam Querrey to pull even at a set apiece and 4-4 in the third.

Exactly two hours into their fourth-round match at the U.S. Open, the 55th-ranked Querrey was tied with the No. 1-ranked Nadal -- a man who owns five Grand Slam titles.

"You know," Querrey would say later, "I felt like I was right in that one."

Indeed he was, to the surprise of pretty much everyone but Querrey. The 20-year-old Californian managed to match the relentless Nadal stroke-for-stroke for long stretches, before losing 6-2, 5-7, 7-6 (2), 6-3.

He actually led briefly, when it was 5-4 and 6-5 in the third set, but he couldn't keep up in the ensuing tiebreaker.

Then, with Nadal serving at 4-2 in the fourth, Querrey made the reigning French Open, Wimbledon and Beijing Olympics champion work rather hard.

"Not the worst thing in the world -- going out to the No. 1 guy," Querrey said.

"I thought I was maybe going to lose, like, (6-2, 6-2, 6-0) or something," Querrey added. "After I broke him in 5-4 at love in the second set, then I started having a little more fun. From that point on, it was awesome."

GO FISH: Never before past the second round at the U.S. Open, Mardy Fish reached the quarterfinals by dismissing Gael Monfils 7-5, 6-2, 6-2 on Monday.

The No. 32 Monfils, a French Open semifinalist this year, is the third consecutive seeded player Fish has defeated, after No. 9 James Blake and No. 24 Paul-Henri Mathieu .

The secret to this success?

"The mental side of the game is huge. I've certainly lost my fair share of the matches because of that, because of not being as mentally tough as some other guys," Fish acknowledged. "I know that, and I think it's -- hopefully, it's in the past."

On Monday, he went to the net 69 times and won 45 of those points; Monfils, in contrast, was just 3-for-12 up there. Fish figures that strategy should fare well against his quarterfinal opponent: the top-ranked Nadal.

DOUBLE TROUBLE: American twins Bob and Mike Bryan became the highest-seeded team in the U.S. Open men's doubles quarterfinals when they won Monday and the No. 1 pairing of Daniel Nestor of Canada and Nenad Zimonjic of Serbia lost.

Nestor and Zimonjic, the Wimbledon champions, were upset 6-4, 6-7 (11), 6-2 by Robert Lindstedt of Sweden and Jarkko Nieminen of Finland, an unseeded duo. The No. 2-seeded Bryans, meanwhile, beat Michal Mertinak of Slovakia and Lovro Zovko of Croatia 6-3, 6-2.