KEY BISCAYNE, Fla., March 24—On match point, Martina Hingis served, charged forward and smacked a volley into the net. She stared at the ball and kicked it in mock frustration, then broke into a big grin.

 Hingis had a large margin of error, and she won the next point to beat Barbara Schett, 6-1, 6-1, today in the quarterfinals of the Lipton Championships.

 The world's top-ranked player has looked first-rate, losing just 11 games in four matches. Hingis's latest victory took 43 minutes.

 "I love it," she said. "You can go do something else if you know you played a great match. I'm going to have a massage."

 Hingis's opponent in the semifinals will be Serena Williams, who wore down Amanda Coetzer, 6-4, 6-0. Williams has won 15 consecutive matches and is bidding for her third straight tournament title, but she is 0-2 against Hingis.

 "I have some business to take care of," Williams said.

 In the men's quarterfinals, Francisco Clavet eliminated Nicolas Kiefer, 7-5, 6-3, and Sebastien Grosjean won a battle of unseeded players by beating Dominik Hrbaty, 6-3, 5-7, 6-1. For the first time in the Lipton's 15-year history, there will be no Americans in the men's semifinals.

 Hingis, who leads the WTA Tour with 21 victories this season, regained the No. 1 ranking last month. Last year she lost in the semifinals of the French Open, Wimbledon and the U.S. Open, then lost the No. 1 ranking to Lindsay Davenport. Chastened, she prepared for this year by training with Nick Bollettieri in Bradenton, Fla.

 "That was the first time after a long time that I really worked for two weeks, day after day, three or four hours of tennis," Hingis said. "I lost some weight, and that was like the best thing I could do. You stop growing, and you start growing to the side."

 Hingis regained her remarkable sense of anticipation. Her serve and forehand are more powerful than before.

 "You can see it," she said. "I mean, I'm back to number one. The scores tell it."

 Results against Schett suggest considerable improvement. Hingis needed a third-set tiebreaker to beat the Austrian in the Australian Open -- which she won -- in January. Today's match was a rout.

 "I was a much better player today," Hingis said. "I took her much more seriously than I did in Sydney. I was always one point better."