In one 9 1/2-hour marathon Saturday, tennis fans were not only treated to the best players, but to every style of play.

In John McEnroe and Martina Navratilova, the two defending champions, the attack-whenever-possible approach was seen at its best. Both are left-handed and can execute every shot.

In the first men's semifinal, McEnroe won because Mats Wilander could not withstand his persistent aggressiveness. McEnroe served below par for a 51 percent first-serve efficiency and only seven aces, but he never stopped attacking. Whereas Wilander came to the net only 49 times in their five-set match, McEnroe came up 120 times.

The match was won at the net. Playing on a medium-fast cement court with the temperature at 114 degrees, McEnroe was willing to take his chances. He knew he would be passed at times, but he also hoped to convert winning volleys when it counted most.

Of McEnroe's 96 placement winners, 49 were volleys. Of Wilander's 69 total winners, only 20 were volleys. Since McEnroe won only three more total games than Wilander, 25 to 22, McEnroe's strategy clearly paid off. It was McEnroe's first win over Wilander in a Grand Slam event.

In the women's final, Navratilova faced Hana Mandlikova, who was her equal in shotmaking ability but not in power. Mandlikova won, 7-6, 1-6, 7-6, because she played the important points better.

Mandlikova, 23, raced to a 5-0 lead in the first set but barely hung on to win, 7-6. Seldom has a crowd seen such a complete assortment of spectacular strokes from two women finalists. Of the 106 outright winners hit, 49 were at the net -- a marked departure from the traditional women's tennis played from the base line.

Indeed, a new era in women's tennis may have begun today.

The match came down to the third-set tie breaker, where Mandlikova sped to a 6-0 lead. It is always difficult for naturally talented players like Mandlikova to resist "going for it" when an opportunity presents itself. Navratilova's serves fell short and Mandlikova stepped in and ripped cross-court winners. When serving, Mandlikova approached the net and knocked off volleys within two shots.

More important, Mandlikova may have found a way of harnessing her awesome talent. In the past she had squandered it. Though she won the French and Australian championships, and was a U.S. Open finalist twice, she had great difficulty adjusting her game when her strokes were off. But back-to-back victories against Chris Evert Lloyd on Friday and Navratilova on Saturday may have corrected this fault.

The second men's semifinal between Ivan Lendl and Jimmy Connors began at 7:10 p.m. The 80-degree temperature was 26 degrees cooler than the first semifinal. Despite a partially sprained ankle suffered in practice, Connors played about as well as possible. At 6-2, 3-1, 40-0, he began limping from this injury.

Whatever Connors tried, Lendl had an answer. This duel took place at 78 feet; Lendl preferred staying at the base line and Connors seldom got an approachable shot. The sprain severely limited Connors' mobility.

The saddest part of Connors' demise was the half-empty stadium at the end. Many of the fans who had been here so long today simply left when they began sensing an inevitable Lendl victory.

Lendl's 6-2, 6-3, 7-5 victory earned for him a 4 p.m. date with John McEnroe Sunday. Neither has won a Grand Slam event this year. Wilander won the French Open and Boris Becker won at Wimbledon.

Though McEnroe has two good ankles, he will be weary from his five-set marathon. It will be an ideal time for Lendl to win his first U.S. Open.