It was a day of contrasts at Wimbledon. Turbulence alternated with gallantry. Bleakness gave way to patches of sun. On Court 1, there were threatening skies and threatening tempers. John McEnroe and Sandy Mayer snarled and sneered in a match that McEnroe was expected to win and did, 6-3, 7-5, 6-0.

The applause was derisive when, late in the first set, McEnroe slammed a ball across the net. Mayer demanded an apology and that a warning be issued to McEnroe. He got neither.

In the distance today, you could hear the sweet sounds of approbation coming from Centre Court, where Kevin Curren and Tim Mayotte played a match as good as their manners. For both reasons, it was a joy to see. Curren won, 4-6, 7-6 (7-4), 6-2, 7-6 (8-6).

Twice Mayotte served for a set and failed to win it--in the second, when he was up a set, and again in the fourth, when he trailed, two sets to one. When he finally lost the fourth-set tie breaker, having saved three match points, he walked slowly to the net, applauding his opponent.

Curren, who defeated defending champion Jimmy Connors in the fourth round, will play Chris Lewis of New Zealand in the semifinals Friday. Neither has gotten that far before. Curren won the only time they played, on grass in Bechenham, two years ago. Curren is seeded 12th; Lewis is unseeded.

McEnroe, the No. 2 seed, will play No. 3 Ivan Lendl. The last time they played, in Dallas this spring, McEnroe won a tempestuous, racket-flinging match (he is 2-0 against Lendl this year but 4-7 lifetime). Soon after, Lendl vowed that if the umpires did not stand up to McEnroe, he would "take matters into his own hands."

Those were precisely the words Mayer used today. But he never had the match within his grasp. McEnroe may not have played "terribly well," as Mayer said, but he played the big points very well, far better than Mayer, who double-faulted to give McEnroe the first break of the match in the first set.

McEnroe served for the set at 5-3. Angry for missing first serves, he berated himself and got in trouble. He saved one break point when Mayer stepped inside a second serve and returned a forehand wide. He double-faulted to give Mayer another chance and slammed the ball across the net.

Indignant, Mayer approached umpire David Mercer (who fined McEnroe Saturday night for verbal abuse during a doubles match) and said, "Next time, he smashes the ball and it almost hits me, you want me to take matters into my own hands? You don't think he did that violently? How far does he have to go to do it violently?"

Dissatisfied, Mayer went back to the base line and said as loudly as needed, "I accept your apology."

McEnroe's reply was inaudible. "He's a stickler about rules," he said later. "I would have apologized had he not complained. I was about to, but he was at the chair."

Play continued. Mayer still had a break point. Again, as he did so often and so successfully on crucial points, McEnroe served wide to Mayer's backhand and the return went wide. He saved the break point and the set was his.

In the second set, Mayer broke in the second game to take a 2-0 lead, McEnroe broke right back with a backhand topspin lob that Mayer mis-hit into the net. In the sixth game, he had McEnroe down, 0-30, on his serve but failed to break.

Unnerved by McEnroe? "That's what it's all about," he said. McEnroe broke in the 11th game and won the remaining seven games of the match.

Curren, though, was flat and so nervous he could barely move in practice, said his coach, Warren Jacques. Mayotte served for the second set at 5-4 but double-faulted to give Curren a break point. He saved that one but Curren got another. A low backhand return at Mayotte forced a volleying error and the set was even at 5. In the tie breaker, Curren got a minibreak with Mayotte serving at 3-3, then got the decisive edge with a miraculous diving volley off a passing shot.

Mayotte tried to regroup in the third. He had just played the best two sets of his life and was still tied, 1-1. But he lost the third set. In the fourth, Mayotte broke to lead, 4-2, with a backhand cross-court pass. He served for the set at 5-3. Two strong returns made it 0-30. A double fault gave Curren a break point.

Mayotte, who is called "Gentleman Tim" by the British press, slammed his racket into the ground, an understandable transgression. He volleyed the last point into the net and, after Curren held serve twice and Mayotte once, they went to a tie breaker again.

Mayotte fell behind, 3-6, missing too many first serves, unable to handle two of Curren's service winners, his increasingly sure returns. Then Curren began to think about "the situation, being in the Wimbledon semifinals," and faltered.

Mayotte saved one, two, three match points, one with a blistering backhand return of serve. Another came on a luckier shot, a forehand let cord return, and the third, on his own serve, by serving and volleying.

Curren's forehand return down the line left Mayotte sprawled on the ground. Again, Curren served for the match at 7-6. He won it with a service winner that was as close to an ace as possible (he had seven today, 65 in the tournament).

As they walked off, Mayotte said, "You played a great match. We should bow. The queen of Japan is here."

Actually, it was the emperor's son and a princess from India. Whoever they were, they should have returned the bow.