Unseeded John Zahurak, a senior at Calvert Hall High School of Baltimore, defeated top-seeded Stevenson Clarke, 6-2, 6-7, 7-6, last night in the National Amateur Indoor Tennis Championships at the Crystal City Racquet Club in Arlington.

"It's one of my biggest wins," Zahurak said. "It's my first college tournament."

Two area players, both of whom attend Stanford, also had big victories.

First, Washington's Jeremy Semple, seeded 13th, beat No. 6 Dacio Campos, who retired with a sprained ankle while trailing, 4-3, in the second set. Campos won the first set, 7-5.

And, 14th-seeded Danny Goldie of McLean came back from 2-5 in the first set to defeat second-seeded Norm Schellenger, 7-5, 6-4.

In the quarterfinals, Goldie will play No. 7 Ahmed El Mehelmy, who defeated No. 10 Fred Perrin, 7-5, 4-6, 6-4, and Semple will play Zahurak.

Third-seeded Josh Sarner, who beat unseeded Stewart Rozas, 6-2, 3-6, 6-1, will play No. 8 Roberto Saad, who defeated No. 15 Zoran Petkovic, 6-0, 7-5. Paul Annancone, the fourth seed, defeated No. 16 Deanne Frye, 6-2, 6-4; Annancone will play fifth-seeded Phil Tuckniss.

Seven women's seeds advanced to the quarterfinals, with only No. 3 Connie Yowell being extended to three sets, 5-7, 6-2, 6-3, against Annandale's Carol Daniels. Yowell, Yale's top player, will face Princeton's Jan Shelburne, a Walt Whitman High School graduate who defeated Michelle Taylor, 7-5, 6-1. Defending champion Kathleen Cummings won by default over Lisa Dunner of Chevy Chase, who was ill. Second-seeded Joy Cummings beat Becky Callan, 6-0, 6-1.