Qualifier Jana Pospisilova of Czechoslovakia upset second-seeded Helena Sukova, also of Czechoslovakia, 6-3, 6-3, Thursday in the second round of the $200,000 European Indoor women's tennis tournament at Zurich, Switzerland.
Pospisilova, 18, is ranked No. 124, while Sukova is sixth.
"It was my biggest success so far," said Pospisilova, who lost this year's European Junior final to Conchita Martinez of Spain.
In other matches, top-seeded Pam Shriver downed Jonna Jonerup of Sweden, 6-0, 6-3; Brenda Shultz of the Netherlands defeated Dinky Van Rensburg, 6-4, 2-3, retired, and eighth-seeded Raffaella Reggi of Italy beat Wiltrud Probst of West Germany, 6-2, 4-6, 6-2.
Second-seeded Boris Becker of West Germany struggled past Carl-Uwe Steeb, also of West Germany, 6-7, 6-1, 6-2, and advanced to the quarterfinals of the Seiko tournament at Tokyo.
"After a 6- or 7-week layoff, I expected a tough game like today," Becker said. "Steeb played very well. I started slow, but I was getting better and better in the second and third sets. That's good for me."
In other matches, top-seeded Stefan Edberg ousted Chris Pridham of Canada, 6-1, 7-5; Shuzo Matsuoka of Japan overcame Marty Davis, 7-5, 7-6, and Paul Chamberlin upset No. 7-seeded Slobodan Zivojinovic of Yugoslavia, 6-4, 3-6, 6-3.
Qualifier Richey Reneberg upset fifth-seeded Magnus Gustafsson of Sweden, 7-5, 6-3, in the second round of a $205,000 Grand Prix men's tournament at Vienna.
In other matches, third-seeded Andrei Chesnokov of the Soviet Union downed Andres Vysand, also of the Soviet Union, 7-6, 6-1, and Christian Bergstroem of Sweden was ill and defaulted to No. 2-seeded Jonas Svensson, also of Sweden.