The day began with that "final" feeling. Margaret Thatcher, the British prime minister, had come to see John McEnroe and Ivan Lendl play what everyone thought would be the match of the day, perhaps the match of the tournament.

Politicians are accustomed to upsets and so is everyone else who has followed this Wimbledon. What Thatcher saw, after McEnroe did the expected and beat Lendl, was a semifinal that will be remembered as one of the best of the decade, in part because it was so unexpected.

She saw Chris Lewis, an unseeded player from Auckland, New Zealand, beat Kevin Curren, in a match that was stunning in its play and its result. Lewis, the No. 91-ranked player in the world, won 6-7 (7-3), 6-4, 7-6 (7-4), 6-7 (3-7), 8-6. She saw two men diving, chasing, scrambling for every get, to get something they never expected to reach, the final of Wimbledon. She saw Lewis come back from a break down in the fifth set, with the help of the umpire who made a controversial call on break point with the score tied, 6-6. She saw him save three break points as he served for the match a game later.

Lewis becomes only the eighth unseeded player to reach the men's final, the first since Wilhelm Bungert in 1967. None of them has won.

McEnroe and Lendl weren't bad, either. McEnroe relied heavily on his wide-kicking left-handed serve and served one of the best matches of his career. He beat Lendl for the third time this year, 7-6 (7-5), 6-4, 6-4, to advance to his fourth Wimbledon final.

Though Labor is out of power in Britain, the left will be heavily favored Sunday when Lewis plays McEnroe. Lewis is zero for two against McEnroe.

Curren, who eliminated defending champion Jimmy Connors, was asked what it would take to beat McEnroe. "I think (Bjorn) Borg will have to come out of retirement," he said.

McEnroe said he was happy to see the prime minister come out and "see two conservative guys play tennis."

They were anything but conservative. McEnroe, who felt he had not been playing aggressively enough on grass, channeled his aggression perfectly. There were no explosions except on his serve--he had 16 aces. He was good on 62 percent of his first serves, to Lendl's 73 percent. But his second serve was the difference.

On grass, McEnroe still maintains the territorial imperative. And there is no love lost between these two athletes. The last time they played, Lendl vowed to hit McEnroe with tennis balls if he continued his antics. McEnroe staked out his turf early, in the sixth game of the first set. With Lendl serving to draw even at 3-3, McEnroe sent a forehand passing shot at Lendl's face.

Lendl thought it was deliberate. "I also think it was perfectly all right," he said. "After that, I was aware he might go down the middle. It makes you more careful. Two or three chances he had to do it again, I had to think about it."

It gave McEnroe one more option, forehand, backhand, down the middle, down his throat.

Twice in the set, Lendl had break points, and both times McEnroe saved them with unexpected serves to Lendl's forehand that went for service winners.

The set could not have been any tighter. There were no breaks. Lendl gave up only six points on his serve before the tie breaker and took a 3-1 lead in it. McEnroe made it 3-2 with a backhand topspin lob. Then, Lendl's discomfort at the net betrayed him. He netted a high backhand volley. "I wanted to keep it down," he said. "I kept it too down."

McEnroe won the next three points to lead, 6-3, and won it the first time he had a chance to serve for the set.

The only break in the second set came at 3-3 on a double fault, as Lendl went for a big second serve and missed. "When a guy hasn't won a Grand Slam (event) and he knows it and he knows I'm playing reasonably well, a serve and volley type game, you're hoping that something like that will occur," McEnroe said.

Though this was by far Lendl's best performance on grass, he was just that tentative in his volleys, that much off in his timing on passing shots and returns. "The difficulty on grass is that when you are reaching for the serve, you can not just put the racket there and hope the ball will stay low," he said. "On other surfaces, you can just put it there and block it."

In the third set, he had McEnroe down, 0-30, in each of the first three games he served and "was not able to take advantage." McEnroe did and that was the difference.

They walked off the court without saying a word to each other. One sensed that the best part of the show was over. Few expected much from Lewis and Curren, two relative unknowns before the tournament. Lewis had not done anything noteworthy since he was the world's No. 1 junior, and junior Wimbledon champion, in 1975. Today, he returned better and served harder.

Lewis looked like a goalie in net, diving about Centre Court. Curren had a chance to take a 2-0 lead in sets but lost four break points in the last game of the second set.

Curren seemed depleted in the third set. But at 2-3 in the fourth set tie breaker, he seemed to find a second wind. He won the last five points, two with devastating backhand returns, and charged into the fifth set replenished. He took a 3-0 lead, then "got a little nervous."

He played a sloppy game at 3-1 and was broken, missing an an easy high forehand volley and hitting another one long. It was then, Curren said, that Lewis "played the game of his life."

To say he saved two break points in the game points is accurate. It is also not enough. At 15-15, they played a point that left both sprawling on the ground, as Curren lunged for a forehand volley that passed Lewis, who was still prone from the volley he had sent the other way.

The crowd gasped. It got better. Their play defied imagination. The sun came out. Lewis saved two break points. They stayed even until 6-6. Of course, there was no tie breaker.

Curren served and fell behind, 0-40. Umpire Steve Winyard asked for quiet. Lewis sent a backhand return down the line that the linesman called wide. Winyard overruled. "The ball was on the line," he announced, calling it good. "According to the people who saw the replay, it was out," Curren said. "After four hours, he chose to overrule. The rule says you overrule when it is clearly out. If that ball was in, it was in by a centimeter. Obviously, I was upset. What a time."

Lewis served for the match and saved three break points. A backhand cross-court let-cord passing shot that hit Lewis' racket and flew high into the air gave Curren his last chance. But Lewis saved with a lunging forehand volley and landed, once again, on his stomach. An ace on a second serve that bounced under Curren's racket gave him match point. Curren mis-hit a backhand and it was over.

Lewis waited as Curren gathered his things. They walked off, making the required bow. It was the only thing Lewis did halfway all day. He said it came "down to the fitness factor. I'm cut and I'm bleeding. I opened old wounds." And healed others.