NEW YORK (Reuters) - World number one Martina Hingis was forced to suffer some of the indignities usually reserved for lesser players at the U.S. Open but the end result was another straight sets win Friday.

The Swiss teen-ager smiled through a 6-3, 6-1 third-round demolition of German qualifier Sandra Kloesel, but only after being made to wait for Tommy Haas to finish his marathon match and trudging across the sprawling tennis center to the old stadium.

``You get a warm-up by just walking down there,'' Hingis said after being pushed off the tournament's main stage for the first time this year.

Hingis was not happy about waiting around while the men's 14th seed turned a potential easy win into a three-hour, five-set marathon.

``We were already ready to go on court, then fourth set, fifth set,'' said Hingis by way of explaining how she managed to lose all of three games in the first set. ``Then in the second set I was getting better.''

Haas may have made life difficult for himself and Hingis before pulling out a 6-3, 6-2, 2-6, 6-7, 6-1 second-round victory over Argentine Mariano Puerta, but at least he came through on a day that saw three seeded players bite the dust.

The women lost eighth-seeded former Wimbledon champion Jana Novotna and 13th seed Dominique Van Roost of Belgium.

Novotna, who has never fully recovered from an ankle injury she sustained at the French Open, fell 6-3, 6-2 to former top-10 player Anke Huber of Germany.

``I'm not the same player I was before the injury,'' said Novotna, who admitted to rushing back too soon to defend her Wimbledon crown. ``My movement is not the same, no matter how much I'm trying.''

Van Roost was bounced 7-5, 6-0 by seasoned veteran Mary Joe Fernandez, a two-time Open semifinalist who conceded just seven points in the second set.

On the men's side, 16th seed Nicolas Lapentti of Ecuador was picked off by elated 148th-ranked Swedish qualifier Fredrik Jonsson 6-4, 5-7, 6-4, 7-5.

``He was the one that went for his shots. He was more aggressive. I was under pressure all the time. I'm very disappointed with the way things went today,'' said Lapentti, whose ranking skyrocketed from 92nd to 16th this year.

Lapentti, seeded for the first time at a Grand Slam after winning Indianapolis last month, had figured to make it to the quarter-finals after potential fourth-round opponent Pete Sampras withdrew with a back injury.

That leaves seventh seed Todd Martin and ninth seed Greg Rusedski as the only seeds in the top quarter of the draw and the two appear to be on a fourth-round collision course after posting comfortable second-round wins Friday.

Martin came through with a big finish for a 6-4, 6-3, 3-6, 6-1 win over sometimes U.S. Davis Cup teammate Richey Reneberg.

Rusedski, the 1997 runner-up, stamped himself as the man to beat in the top half of the draw with a dominating 6-4, 6-3, 6-1 victory over David Prinosil of Germany.

``If I play like that for the tournament, I think I'll be in good shape. You can't play much better than that,'' said Rusedski.

He certainly made a believer out of Prinosil.

``If his serve is working he can beat anybody,'' Prinosil said of the big left-hander who appears to have fully recovered from a recent foot injury. ``He's in very good shape. He's moving well. He was very fast on the net.''

Fernandez earned a meeting with third-seed Venus Williams, the 1997 runner-up who advanced by a walkover when Henrieta Nagyova withdrew with a wrist injury.

``She does everything well. There's not really a huge weakness in her game. It's tough,'' Fernandez said of her fourth-round assignment.

Huber next faces the winner of a night match between Australian Open runner-up Amelie Mauresmo of France, the 15th seed, and unseeded American Tara Snyder.

Hingis will take an 11-match winning streak over Arantxa Sanchez-Vicario into her fourth-round match with the 10th-seeded Spaniard.

Sanchez-Vicario, the 1994 Open champion, advanced to the round of 16 for the 12th consecutive year with a surprisingly easy 6-2, 6-2 drubbing of 18th-ranked Patty Schnyder of Switzerland.

Also moving into the round of 16 with ease was 12th-seed Austrian Barbara Schett, who crushed Spaniard Virginia Ruano Pascual with the loss of just one game.