Unseeded Pam Shriver of Baltimore upset sixth-seeded Natalia Zvereva of the Soviet Union, 6-2, 6-0, yesterday in the opening round of the Toray Pan Pacific Open tennis tournament in Tokyo.

Shriver, still troubled by a shoulder injury that required surgery last June and sidelined her for the rest of the year, showed a strong serve-and-volley game in gaining the surprisingly easy victory on an artificial surface.

"I need one or two months to completely recover from the injury. I still felt a little sore," Shriver said.

Defending champion Steffi Graf and Australian Open winner Monica Seles had first-round byes. . . .

Seles will lead Yugoslavia's team in the Federation Cup competition in Nottingham, England.

The International Tennis Federation said 18 of the world's top 20 women's players have been nominated to play in the July 21-28 event.

The United States, which beat the Soviet Union in last year's final, nominated Mary Joe Fernandez, Jennifer Capriati, Zina Garrison and Gigi Fernandez, with Amy Frazier and Meredith McGrath as reserves.

Jana Novotna, who beat Steffi Graf on her way to the Australian Open final, will head the Czechoslovakian team, and Graf was named to lead the German team.