San Querrey signs autographs after defeating Ivo Karlovic in the U.S. Open. Querrey won his match, 7-6 (5), 7-6 (5), 6-2, on Saturday in New York.

New York ? Sam Querrey is so young that there isn’t a trace of irony when he mentions growing up rooting for Andy Roddick and James Blake, two guys still very much on tour and still in their 20s.

Querrey is so new to this whole professional tennis gig that there is nothing but earnestness in his voice when he admits he’s excited his matches are on TV.

And Querrey is so young, so new and so eager that he clearly means it when he plainly explains he’s “looking forward” to facing No. 1 Rafael Nadal at the U.S. Open, a matchup the 20-year-old Californian set up Saturday by knocking off a seeded player for the second time in the tournament.

It’s Querrey’s first berth in the fourth round of a major championship.

“And, you know, it’s great that it’s the U.S. Open,” Querrey said, words tumbling forth through a wide grin. “It’s the one that, you know, if I had to pick one to win, it would be this one.”

Heady talk for a kid who is ranked 55th, owns one career title and has lost more matches than he’s won on tour – even after upsetting No. 14 Ivo Karlovic, 7-6 (5), 7-6 (5), 6-2, in the third round Saturday.

Querrey added that to his victory over No. 22 Tomas Berdych in the first round. A far tougher test follows, of course: Wimbledon, French Open and Olympic champion Nadal, who won for the 41st time in his last 42 matches by brushing aside Viktor Troicki, 6-4, 6-3, 6-0.

Querrey was hardly the only man to author a surprise Saturday, capped by Mardy Fish’s 6-3, 6-3, 7-6 (4) victory over No. 9 Blake in an all-American match at night. Fish took the last five points to earn his first berth in the fourth round at the U.S. Open.

In other third-round action Saturday, French Open semifinalist Gael Monfils, seeded 32nd here, beat No. 7 David Nalbandian in straight sets.

No. 6 Andy Murray of Britain came all the way back from a two-set deficit to defeat a fading Jurgen Melzer of Austria, 6-7 (5), 4-6, 7-6 (5), 6-1, 6-4.

In women’s play, No. 6 Dinara Safina had to overcome a big deficit before getting past 60th-ranked Timea Bacsinszky of Switzerland, 3-6, 7-5, 6-2, at night. No. 7 Venus Williams compiled a remarkable 32-4 edge in winners against No. 27 Alona Bondarenko of Ukraine. No. 4 Serena Williams – one of five women with a shot at moving up to No. 1 by tournament’s end – was never troubled by No. 30 Ai Sugiyama of Japan.