Pablo Arraya, mixing strong forehand slams with unnerving drop shots, upset third-seeded Mats Wilander, 7-6 (7-4), 7-6 (7-5), in straight sets yesterday in the third round of men's singles at the $450,000 U.S. Open Clay Courts tennis tournament.

Arraya, 20, is a member of Peru's Davis Cup team although born in Argentina. He has never won a major championship as a professional.

Wilander, 17, the Swede who is ranked ninth in the world after winning the French Open this year, was leading, 5-4, and within one point of taking the second set. But Arraya held serve and tied the set at 5-5 and 6-6 before winning the tie breaker. Four of Arraya's winning points in that tie breaker came on backspin drop shots that Wilander was unable to reach.

"Usually my drop shot is not that good, but I was playing out of my mind . . . I was kind of surprised," Arraya said, grinning . . .

Top-seeded Kate Brasher of Great Britain defeated Sharon Hodgin, 6-1, 6-3, and Sue Rasmussen of Oakton, Va., and Kristie Reynolds of El Cajon, Calif., survived two tie breakers to gain the doubles quarterfinals of the Toyota Women's Classic at Landon High School.

Rasmussen and Reynolds defeated Paula Coulter of Denver and Lani Wilcox of Las Vegas, 7-6 (7-5), 7-6 (8-6) . . .