Ivan Lendl overcame Gary Muller, and John McEnroe outdueled Wally Masur last night as the top four seeds advanced to the quarterfinals of the U.S. Pro Indoor tennis tournament in Philadelphia.

Lendl, the No. 1 seed, defeated 15th-seeded Muller, 7-6 (7-5), 6-3, and McEnroe, seeded fourth, edged No. 13 Masur, 7-6 (7-2), 6-4.

In other matches, defending champion and second-seeded Pete Sampras survived three set points to defeat MaliVai Washington, 6-3, 7-6 (9-7), and No. 3 Brad Gilbert shook off a bad start to beat No. 14 Paul Haarhuis, 7-6 (7-3), 6-1.

Lendl struggled in the first set. He broke Muller's serve to lead 6-5 with a backhand passing shot, but was unable to win the next game, double-faulting on game point. In the tiebreaker, Lendl needed two set points before Muller volleyed a shot into the net.

McEnroe and Masur both held serve throughout the first set. McEnroe then dominated the tiebreaker, winning the first five points and reaching set point at 6-2 when Masur returned a serve into the net. With both players at the net, McEnroe ended the spectacular exchange with a running volley.

In the second set, McEnroe broke Masur's service in the first and fifth games, with Masur returning the favor in the fourth game. Masur pulled ahead 30-love in the 10th game before two wild shots turned the tide. McEnroe rushed the net for a forehand drop shot to reach match point, then hit a service winner to claim the victory.

Donnay Indoors: In Brussels, Boris Becker and Stefan Edberg each fought off a strong challenge before advancing to the quarterfinals.

Becker, the world's top-ranked player, need two tiebreakers to defeat Eric Jelen, 7-6 (7-2), 7-6 (7-5), and No. 2 Edberg was taken to three sets by Pat Cash, 3-6, 6-1, 6-4.

Also advancing were Jakob Hlasek and Andrei Chesnokov. Hlasek, seeded eighth, defeated Mats Wilander, 6-1, 7-5, and No. 6 seed Chesnokov beat Goran Prpic, 6-4, 7-6 (7-2).

Virginia Slims of Chicago: Top-seeded Martina Navratilova took 50 minutes to overpower Anne Smith, 6-1, 6-2, and gain the semifinals.

Seeking her 11th Chicago Slims title, Navratilova meets the winner of today's match between fourth-seeded Jennifer Capriati and No. 6 Helena Sukova.

Sukova won her second-round match, 6-2, 6-2, over Kathy Rinaldi.

Earlier, Zina Garrison beat Rosalyn Fairbank-Nideffer, 6-2, 6-2.