U.S. Open champion Pete Sampras beat fellow American David Wheaton in a tight serve-and-volley match yesterday to reach the semifinals of the $1.1 million Stockholm Open tennis tournament.

Sampras, 19, playing his first ATP Tour event since becoming the youngest U.S. Open champion in history Sept. 9, won, 7-6 (7-3), 5-7, 6-4, on the fast Supreme Court.

Alexander Volkov of the Soviet Union joined Sampras in the semifinals, beating 1989 world junior champion Nicklas Kulti of Sweden, 6-2, 6-1, in a match between unseeded players.

Saturday, Sampras, who rested for three weeks last month because of shin splints, will meet No. 2 seed Boris Becker of Germany, who beat Goran Ivanisevic of Yugoslavia, 6-4, 6-2.

In the other quarterfinal last night at the Globe Arena, Stefan Edberg, the world's top-ranked player, outlasted Brad Gilbert, 6-4, 3-6, 6-1. . . .

Steffi Graf needed a few extra games but scored her 12th consecutive victory over Nathalie Tauziat, 6-2, 6-4, to move into the semifinals of a WITA indoor tournament in Brighton, England.

Today, Graf will meet Catarina Lindqvist of Sweden, who beat Italy's Cathy Caverzasio, 6-2, 6-3. Third-seeded Helena Sukova also moved into the semifinals with a 6-1, 6-1 victory over Sara Gomer of Britain. . . .

Second-seeded Jennifer Capriati dominated Maria Strandlund, 6-1, 6-4, to advance to the semifinals of the Puerto Rico Open in San Juan against No. 6 Gigi Fernandez.