As he is wont to do, Boris Becker went for an ace on match point today.

Across the net at the U.S. Clay Court Championships stood Miloslav Mecir, who had beaten him soundly in Rotterdam four months ago. Becker, serving for the match at 40-30, did as he almost always does on big points and went for a big serve. Mecir just got his racket on it, the ball sailed out, and Becker won his 16th straight match, 6-2, 7-5, advancing to a semifinal Saturday against top-seeded Ivan Lendl, who beat No. 8 Martin Jaite, 6-2, 6-3.

"I didn't think it was a good match, but I am happy that I beat him," said Becker, who seems to judge a match by its aesthetics for the spectators. "I think we made too many mistakes. We sometimes had good rallies but sometimes we missed."

Defending champion Andres Gomez and No. 4 seed Yannick Noah also won today and will play in the other men's semifinal Saturday. In the women's draw, Andrea Temesvari and Zina Garrison won to earn a place in the final Saturday (WDVM-TV-9, 1 p.m.).

Although his serve came through on match point, Becker could not rely on it as much as he usually does. In the Wimbledon final, he had 21 aces. Today, he totaled three aces and service winners against Mecir, who plays a steady, almost lethargic base-line game.

"My serve didn't come today," Becker, the third seed, said. "This means that I can also play good from the base line, without my serve. It shows me I can beat a player like Mecir from the base line. It does a lot for the confidence."

Confidence is one thing Becker doesn't seem to lack. Earlier in the week, Hans Schwaier, his West German Davis Cup teammate, said Becker thinks he can beat anybody. After his match today, Becker said he wanted to play Lendl, not Jaite.

"I've never played him (Lendl)," said Becker. "I'd like to see what I could do against him."

Lendl lost only five points on serve in the first set, breaking Jaite in the third and seventh games.

Jaite's only break came in the second game of the second set when Lendl became upset over two calls and refused to play until the umpire left his chair to check a mark. The umpire upheld the call against Lendl and Jaite took a 2-0 advantage. But Lendl broke Jaite on two of his next three serves for the match.

Becker went ahead quickly in the first set, breaking Mecir in the third game. Mecir, ranked 13th in the world, got a double break point in the sixth game, but Becker came back to deuce, then held. Becker went up, 5-2, with a break, then held to win the set.

Mecir had double break point in the fourth game of the second set, but Becker came back, pulling out a service winner to hold. Becker broke Mecir in the ninth game to go up, 5-4, but Mecir broke back. Becker broke again to go ahead, 6-5, and served out the match.

Garrison and Temesvari will meet in a rematch of the 1983 final, which Temesvari won, 6-2, 6-2.

Garrison, the No. 2 seed and the only U.S. player remaining in the tournament, defeated third-seeded Gabriela Sabatini, 6-4, 6-2.

Temesvari, who had lost eight of 11 matches, was a 6-3, 6-4 winner over Kate Gompert, who had upset No. 1 seed Manuela Maleeva Thursday.

Gomez advanced to his first semifinal since early April by defeating Jaro Navratil, 6-2, 6-3.

Three times in his last four tournaments, Gomez had lost his first match. Last week at the D.C. National Bank Classic, he was the No. 2 seed and defending champion but lost to Pablo Arraya in the second round after receiving a bye.

"I've been waiting for some months to get a break and try to do well in a tournament," said Gomez, who has been troubled by an injury to his left shoulder. "I'm very confident now. For me, it's harder to win my first-round match than to win in the semifinals."

Gomez has won the first two times they played, but Noah, who won the D.C. National Bank Classic Monday and has played well lately, took their last meeting.

Noah advanced today by defeating Schwaier, 6-3, 6-1. Earlier today, Noah had to complete a third-round match with Diego Perez that was halted by rain Thursday night with Noah leading, 6-1, 1-0. He won that, 6-1, 6-3, but with the prospect of two doubles matches later in the day ahead of him, Noah and partner Guillermo Vilas forfeited.