Hingis advanced to a quarter-finals date with American Chanda Rubin, a 6-4, 6-4 upset winner over seventh seed Amanda Coetzer of South Africa. Seles was swept out of the tournament by Slovakian Henrieta Nagyova 6- 2, 6-4 in the third round.
Hingis had few problems in beating fellow-Swiss Schnyder in just 54 minutes. Moving swiftly and counterpunching brilliantly against the left-hander, the 18-year-old Hingis forced Schnyder to go for outright winners, which the 20-year-old rarely made.
Schnyder, seeded 10th, made 25 unforced errors against only 13 winners. "I tried to play aggressive, it's the only way to beat her," Schnyder said. "I made too many mistakes. I was risking too much. I was dominating a lot of the points, but I missed when I had to go for a winner. She was running down all the balls and reacting well. She could read my game a little."
Hingis, who now has a 2-1 record against Schnyder, said that it was the best she had played against her.
"Reading my opponents is my strength," Hingis said. "Most of the time that is my weapon on the court. I pretty much know where the players want to go. That's why I'm number one."
Two months ago Schnyder controversially fired her coach and hired the mysterious German nutrition guru Rainer Harnecker. He has put her on a radical diet but Schnyder admits she is not firing on all cylinders.
"I'm less confident," said Schnyder, who won five titles last year. "I've had a hard time and I couldn't concentrate the way I wanted to. But I can handle the situation better right now."
Schnyder said she believes her new diet, which includes drinking two to three litres of orange juice a day, will make her a better player in the long run. "For sure." she said. "Otherwise I wouldn't do it."
Seles looked completely out of sorts against the 20-year-old Nagyova, a tall, powerful player who made her opponent appear slow-footed and confused.
Nagyova has won five titles in her career but had never beaten a top- 10 player. "It was for sure some of the best tennis I have played," the 27th-ranked Nagyova said. "I played what I was thinking, some slice, not hitting balls so hard, a little bit clever and I was mentally fit."
Seles was making her first appearance at Indian Wells since 1992, when she won the title. While she reached the semi-finals of the 1999 Australian Open, Seles has only played three events this year and hasn't won a title in five months.
"My mind wasn't there," Seles said. "She really didn't give me a chance to get into it. My head wasn't there, my game wasn't there. I was just pushing the ball back." When asked why her mind wasn't in the match, Seles snapped, "That's for me to ponder."
Nagyova's opponent in the quarter-finals will be 12th seed Sandrine Testud, who beat fellow Frenchwoman and eighth seed Nathalie Tauziat 7-6, 6-2.
Andre Agassi, the ninth seed, withdrew from the men's tournament, the $2.45 million Newsweek Champions Cup, because of a right hamstring strain. He suffered the injury on Saturday during a semi-final loss to Jan-Michael Gambill in the Franklin Templeton Tennis Classic in Scottsdale, Arizona.
Agassi's spot in the draw was taken by "lucky loser" Fernando Meligeni of Brazil.