The last time John McEnroe and Jimmy Connors played a semifinal at the U.S. Open, they dueled for five sets through the sun and the dusk and it wasn't enough to resolve the differences between them. McEnroe needed a fifth-set tie breaker to separate himself from Connors. That was in 1980 and McEnroe won the Open for the second of three times.

The last time they played at Wimbledon, three months ago, McEnroe needed only 80 minutes to dismantle Connors' game. His mastery was such that Connors could afford to be good humored about it.

The rivalry resumes Saturday when McEnroe and Connors will meet again in the semifinals of the U.S. Open. The rivalry is rich with possibilities. McEnroe grew up minutes from the stadium but is treated like an expatriot here. Connors, who has won the last two years and five times altogether, claims New York as his own.

Connors has beaten McEnroe 12 times but not once in the last year. McEnroe has won 16 times, including the last seven.

"John has to play subpar to lose anytime to anyone right now," said Gene Mayer, who lost to him Thursday night.

Connors, who never concedes anything, conceded nothing Thursday night. "Everytime is a new time and you just go out there and forget about what happened the last time," he said.

"He's got nothing to lose," McEnroe said. "He's going to have a lot of people on his side. Normally, there should be a lot more pressure on him because he's trying for a third straight Open. Normally, he would feel the pressure from that, but because of the fact that I'm ranked No. 1 now and I've beaten him this year quite a few times, the pressure's really off him."

The confrontation between them, between the deft serve and volleyer and the indominitable base liner, is classic, and it overshadows the other semifinal between Ivan Lendl, of Czechoslovakia, and Pat Cash, of Australia.

Someday, perhaps, their rivalry will be anticipated with as much relish. But right now it is only two matches old. Lendl won both, a fourth-round match at Wimbledon last year and a fourth-round match at the Australian Open. Both were played on grass, a surface that should favor Cash.

At 19, he is Australia's hope for the future and only reminder of its glorious past. He is a serve and volleyer and he played one of the best matches of the tournament when he beat the fourth seed, Mats Wilander, in the quarterfinals. This should give Lendl pause.

Twice before, Lendl has cruised through the semifinals, with straight-set victories over McEnroe and Jimmy Arias, only to crash ignominiously in the final, a victim of his own jitters and Connors' relentless determination. He tries not to sound haunted. Surely, he wants another chance.