New York ? Hardly at her best, barely beating one of the tour’s pesky teens, Serena Williams suddenly found herself face-down at the U.S. Open.

Running for a ball she couldn’t reach, the six-time Grand Slam champion slipped and planted both palms on the court to brace herself. Williams shook the sting out of her hands, beckoned a ball boy to retrieve her fallen racket, then took her sweet time before facing break point.

Recomposed, Williams smacked a service winner at 111 mph, an ace just as fast, and forced an error. Just like that, she held serve en route to beating 30th-seeded Tatiana Golovin, 7-5, 6-4, Friday night to reach the Open’s fourth round.

“I was playing two opponents: her and myself,” Williams said.

Defending champion Andy Roddick followed them out on court and, overcoming the third-set distraction of a diatribe directed at the chair umpire, beat 18-year-old Rafael Nadal of Spain, 6-0, 6-3, 6-4, to get to the third round.

Roddick tied his Open record with a 152 mph serve that made Nadal whiff and, after losing the opening two points, won 23 of 27 to seize control. One of Roddick’s big serves caught Nadal in the lip, and another left the teen tumbling. Roddick hit the deck once, too, scraping skin off his hand as he slipped while charging the net.

His biggest problem was staying focused. Roddick noticed pal Rulon Gardner, a 2000 Olympic gold medalist wrestler, in the stands. And he expended some energy yelling at chair umpire Andreas Egli for calling a let when a ball dribbled out of Roddick’s pocket during a point in the third set.

Roddick was broken once in that set, then won the last four games.

“I played really well for the first two sets; kind of had a concentration lapse in the third,” Roddick said. “But I was able to come through in the end.”

It was not Williams’ best performance. It brought to mind last month’s loss in the Wimbledon final to Maria Sharapova, who’s 17 — just one year older than Golovin.

Williams, the 1999 and 2002 Open champion, lost four straight games to trail 4-1 in the first set. She made a dozen unforced errors to that point and finished with 42. But she turned things around by winning eight of nine games.

During one changeover when her play was at its roughest, Williams glanced up at the giant video screen hovering over Arthur Ashe Stadium and noticed her total error count.

She made it through, though, as did all the favored women Friday, including No. 2 Amelie Mauresmo, No. 6 Elena Dementieva, No. 8 Jennifer Capriati, No. 10 Vera Zvonareva, No. 15 Patty Schnyder, and No. 16 Francesca Schiavone, who ended wild card Angela Haynes’ run, 6-3, 7-6 (3).

It wasn’t that way among the men, though.

No. 7 Juan Carlos Ferrero (the 2003 runner-up), No. 8 David Nalbandian (a semifinalist last year) and No. 12 Sebastien Grosjean all lost. And No. 23 Vince Spadea’s 6-3, 4-6, 3-6, 6-3, 6-4 defeat against Austria’s Jurgen Melzer left just two of the 18 U.S. entrants still in the draw: Andre Agassi and Roddick.

Never before had fewer than three Americans reached the Open’s third round; for comparison, all three Austrian entrants made it that far this year. One, Stefan Koubek, slipped past Ferrero 7-6 (2), 4-6, 6-7 (6), 6-2, 6-3.

Normally reserved on and off the court, Ferrero got in trouble for slamming a ball out of the arena and for yelling at an official, which cost the Spaniard a point.

Chair umpires “do not treat all players the same,” Ferrero said