Defending champion Hana Mandlikova played her usual matches within a match tonight at the Virginia Slims of Washington at Patriot Center. Just when you thought she would lose to eighth seed Natalia Zvereva, Mandlikova took the last six games of the match to advance to the semifinals with a 5-7, 6-3, 6-3 win.

Mandlikova will face top seed Martina Navratilova, a straight-set winner over Zina Garrison, in one semifinal Saturday evening at 6:30. Mandlikova won the last match between the two, capturing the 1987 Australian Open on grass in straight sets.

But if she plays Saturday like she did tonight, that streak will end very quickly.

"I really played poorly and I still won the match," Mandlikova said. "That's a credit to me. Obviously, if I play like this tomorrow, I won't win."

The other semifinal will pit second seed Pam Shriver against third seed Gabriela Sabatini at 1. Shriver took fifth seed Helena Sukova in 67 minutes, 6-2, 6-3, and Sabatini knocked off No. 7 Barbara Potter, 6-3, 6-2.

Tonight's match was one either player could have won 100 times or so before the 2-hour, 27-minute issue was settled. Mandlikova started it by blowing two set points in the first set, allowing Zvereva, the No. 1 Soviet player, to take the final three games and the set.

"Sure, it was frustrating," Mandlikova said. "But that's the game. I had two set points and I lost it. Plus, I thought that was a bad call there. It was very frustrating. But I just kept hanging in there."

She hung in long enough to break Zvereva in the eighth game of the second set at love, putting away a weak Zvereva backhand. Mandlikova started getting more zip on both her approaches and passing shots, and held at love to take the second set.

But it looked like it would be for naught when Zvereva held at love, then banged a crosscourt backhand service return to convert a break and take a 2-0 lead. Mandlikova looked done for sure when Zvereva recovered from 0-40 and saved two other break points to take the game.

"After 3-love, they didn't have any kind of tension in the game," said Zvereva's coach, Olga Morozova. "After 3-love, she just felt down."

Mandlikova held, then broke for 3-2 when Zvereva's approach hit the net. At 30-30 of the next game, Mandlikova serve and volleyed, dinking to the open court. A slice backhand made it 3-3.

"She thought it was important when it was 3-1 on her serve, and she didn't put one ball in," Morozova said. "It was important, because it still wasn't a very comfortable position for Mandlikova."

All of a sudden, Mandlikova ripped a forehand passer and a forehand crosscourt passer to take a 4-3 lead. She held for 5-3, and Zvereva double faulted at 40-30 of the ninth game. Two unforced errors ended it.

Earlier, Navratilova's victory over Garrison extended Navratilova's streak over Garrison to 21 straight matches, dating back to the 1982 French Open. In 44 career sets with each other, Navratilova has won 42, one of which came in the Slims event in Dallas earlier this year.

"I respect her game," Navratilova said. "I respect her as a person, but mostly as a player. I always get up for her, because I know she gets up for me. I know if I don't play well, she can beat me. She tries to play the game I play, but . . . I tend to overpower her a little bit, even though she hit the ball well. Today, she particularly served much harder than she ever has before. But I was still able to return really well."

In two of their previous three matches, Shriver had beaten Sabatini in straight sets, and said she was losing a little respect for Sabatini's game.

"Then I played her in the finals at Brighton," said Shriver, who has 465 career victories, "and she played a really good match {winning, 7-5, 6-4}. It was good, because I learned that she's playing better and that once again, she has my respect."

In the first set, each was broken on their opening service game, but Shriver took the set by also breaking in the sixth and eighth games.

The second was steaming along toward a tie breaker when Sukova double faulted to fall down 0-30. She battled back, saving a match point at 30-40, and had the game on her racket. But her serve wasn't on the mark, and Shriver ripped a backhand winner on a second serve for another match point. She gave that one back, but converted a third on a perfectly placed lob that Sukova could only watch.

Potter had five break points in the seventh game against Sabatini, the most discouraging being unforced errors on her forehand. Sabatini held for 4-3, then quickly broke Potter and served out the set. Overall, Sabatini won seven of the next eight games after the 3-3 tie. After that barrage, she was up, 5-1, and the match was over.

"I think I played well on the important points," Sabatini said. "The first set was very difficult. "I think I played better in the first set. But in the second set, I don't think she played very well."

Said Potter: "Frustration is the key word today for Barbie Potter. I have to go back and reassess my own effort. I haven't played this kind of competition regularly, and it showed. I should be able to take the punches in the gut, and it was like a jelly belly today."

U.S. Pro Indoor:

Unseeded Jorge Lozano switched from an attacking game to a rallying strategy and defeated 14th-seeded Dan Goldie, 4-6, 6-1, 6-4, advancing to the semifinals of the $600,000 championship tournament in Philadelphia.

John Fitzgerald, the 16th seed who Thursday ousted top seed Ivan Lendl in straight sets, defeated No. 9 seed Kevin Curren, 5-7, 6-4, 6-3, to advance as well. Defending champion Tim Mayotte, the No. 2 seed, eliminated unseeded Jim Grabb, 7-5, 3-6, 6-4, and will play sixth-seeded Christo van Rensburg, a 7-6 (7-5), 6-2 victor over Sammy Giammalva.

Lozano set up the victory by breaking Goldie's service in the third set with the games tied at 4-all. Goldie double-faulted to make it 5-4. Goldie then returned service into the net four straight times to give Lozano the victory.

"I was trying to come to the net, but he returns well," Lozano said of Goldie, the 1986 NCAA champion from McLean. "He likes a fast pace. So I just tried to put my first serve in at three-quarters speed and stay back and rally with him."YESTERDAY'S RESULTS SINGLES Quarterfinals

Gabriela Sabatini (3), Argentina, def. Barbara Potter (7), Woodbury, Conn., 6-3, 6-2; Pam Shriver (2), Lutherville, Md., def. Helena Sukova (5), Czechoslovakia, 6-2, 7-5; Martina Navaratilova (1), Fort Worth, def. Zina Garrison (6), Houston, 6-1, 6-3; Hana Mandlikova (4), Australia, def. Natalia Zvereva (8), Soviet Union, 5-7, 6-3, 6-3. DOUBLES Quarterfinals

Mary Lou Daniels, Chicago-Anna-Maria Fernandez, Torrance, Calif., def. Lea Antonoplis, Los Angeles-Barbara Gerken, Thousand Oaks, Calif., 6-3, 2-6, 7-6 (9-7); Sabatini-Sukova (2), def. Nicole Provis, Australia-Judith Wiesner, Austria, 6-2, 6-3. Navratilova-Shriver (1) def. Natalia Bykova, Soviet Union-Leila Meskhi, Soviet Union, 6-1, 6-2; Zvereva-Larisa Savchenko, Soviet Union, def. Elise Burgin, Baltimore-Robin White (4), San Jose, 6-4, 6-4.

TODAY'S SCHEDULE In order of play AFTERNOON MATCHES (1 p.m.)

Sabatini vs. Shriver; Sabatini-Sukova vs. Savchenko-Zvereva. EVENING MATCHES (6:30 p.m.)

Navratilova vs. Mandlikova; Navratilova-Shriver vs. Mary Lou Daniels, Chicago-Anna-Maria Fernandez, Torrance, Calif.