Stan Smith was leading Jimmy Conner, 3-2, in the fifth set, with an advantage point. All the people crowded around Court 1 at the end of a long gray afternoon sensed that Connors, the top dog, could be had. Smith's heart was racing, just like in the old days. He told himself to be calm.

Smith whacked a good service return and got his [WORD ILLEGIBLE] . He went for it - a hard backhand down-the-line. He thought it was a winner. So, momentarily, did Connors.

Smith started to do an involuntary little dance step of jubilation, but the ball clipped the top of the net and fell back.

"It felt good. I though I had the shot. It even looked like it teetered a little bit," Smith sighed later, after Connors had pulled himself together in a bizarre final set and run out a 7-9, 6-2, 3-6, 6-3, 6-3 victory to advance to the quarterfinals of the Centenary Wimbledon championships.

It was that kind of an afternoon at the All-England Lawn Tennis and Croquet Club. The first Saturday is traditionally the longest day, with furious activity and some surprises, and the midpoint of this wild Wimbledon was no excepton.

"When it was over, the top eight women's seeds had all reached the quarters, as expected, although defending champion Chris Evert had two set points against her at 1-5 in the first set against Greer Stevens, and Billie Jean King lost the first set to another young South African, Marise Kruger.

Evert brushed off the set points with a deep forehand down-the-line that forced a backhand error, and a winning backhand cross-court. That started a five-game run that took the spung out of Stevens, 20, who is bouncy, athletic, and quick enough to be nicknamed "cat."

Stevens started the match by whacking her potent forehand with the dreamlike abandon - "She was unconcious and the ball had eyes," commented one of Evert's relatives who was watching - but eventually she woke up, Evert's overall solidity asserted itself and engulfed Stevens' hit-or-miss aggression. Evert may ultimately be happy about having been pushed, for this match gave a real test to the most improved shot in her formidable arsenal: The backhand volley. She passed splendidly.

King, who has gone out and practiced after her matches because she is unhappy with her fitful form, was down, 1-4, in the first set, leveled, then was broken to fall behind, 4-5. That seemed to set off a spark in her, and she reeled off nine straight games, eventually eliminating Kruger.

King, who needs one title to exceed the all-time career record of 19 in singles, doubles and mixed doubles that she shares with Elizabeth Ryan, now 85, lost today in doubles. She and Karen Hantze Susman bowed to Mary Carillo and Pat Bostrom, 7-9, 6-4, 6-3.

Evert, the No. 1 seed, and King, the six-time singles champion, meet Monday in what should be the women's match of the tournament.

The other pairings in the quarters of the women's singles: Virginia Wade vs. Rosemary Casals, Kerry Melville Reid vs. Sue Barker, and Betty Stove vs. No. 2 seed Martina Navratilova.

While the women's quarterfinal lineup is as expected, the men's has a touch of absurdity, especially in the top half of the draw: Connors vs. Byron Bertram, John McEnroe vs. Phil Dent, Vitas Gerulaitis vs. Billy Martin, and Ilie Nastase vs. Bjorn Borg.

Borg served and smashed ferociously today in wearing down and then knocking out Wojtek Fibak on the center court, 7-5, 6-4, 6-2. The 21-year-old Swede has lost his skittishness and, after a hard day of practice Friday, seems back in the serve-and-volely rhythm that won him the title a year ago.

Nastase has settled down after his controversial five-set victory over Andrew Pattison in the second round, as he often does if he survives one of his tumultous scenes. He played some lovely touch shots today and volleyed surely, if not powerfully, in dispatching Tom Okker, 6-8, 6-4, 6-4, 6-4, in an enthralling match on center court.

Gerulaitis, 22, the Italian Open champion, and McEnroe, 18, believed to be the first qualified ever to reach the quarterfinals here, made it a great day for the Port Washington (Long Island) Tennis Academy.

Both are products of the program there that Gerulaitis, the flamboyant Brooklyn native whose strokes have become as brash as he is says "revolutionized junior tennis in the East by bringing everything the kids in California had - coaching, courts and competition - indoors."

Gerulaitis, whose footwork on the slippery grass of Court No. 2 was remarkable, hit passing shots with Panache and volleyed with a superb touch in a 6-1, 6-4, 3-6, 6-4, victory over Dick Stockton, runner-up to Connors for the World Championship Tennis title last month.

Gerulaitis made some backhand volleys off his shoetops that defied belief, and was quick enough to run down Stockton volleys that would have been winners against any other player except, perhaps, Nastase.

For Gerulaitis, who cramped and lost a five-set match to Stockton in the WCT semis in Dallas, this was a particularly satisfying truimph. Gerulaitis beat Arthur Ashe, the defending champion, to reach the quarterfinals on the same day last year, but for some reason has been unable to convince some "experts" of his abundant talent.

"I was riding home yesterday in my friend's limousine and we were listening to BBC Radio," Gerulaitis related. "They had Fred Perry and three other former champions on, discussing Wimbledon, and they all had their opinions on who would reach the quarters.

"The only thing they all agreed on is the Gerulaitis would lose in the round of 16. That was a unanimous decision and it got me pretty fired up. People have said for two or three years that I can't play on grass, but my serve's improved and I've beaten some pretty good grass-court players. I used to think about beating well-known people. Now I think about winning tournaments, and I'd like to win this one."

McEnroe, a slender lefthander with a flashy topspin backhand, freckles and a good-natured insouciance, does not yet think about winning adult tournaments.

"I was happy just to get in," he said, recalling that he had to survive three qualifying matches to get in the draw because he is only 270th in the computer rankings of the Association of Tennis Professionals.

Today, he played with the free spirit of a kid who has nothing to lose and a lifetime of hot fudge sundaes to gain, and ousted Alex Mayer, 1973 NCAA champion and a semifinalist here when the ATP struck Wimbledon that year, 7-5, 4-6, 6-3, 6-1.

McEnroe, who was playing qualifying matches when his class at Trinity High in New York City graduated earlier this month, is bound for Stanford, Mayer's alma mater, in the fail. He is still an amateur, but now the pro tour is beckoning. "If I win the tournament," he said impishly, "maybe I'll think about changing my plans."

Martin, 20, is another young American who has suddenly found a well-spring of confidence. He saved three match points against Ray Ruffels in the second round, upset No. 3 seed Guillermo Vilas in the third, and today ousted another lefthander, No. 14 seed Mark Cox, coming from 2-5 down in the final set to win, 3-6, 6-3, 6-4, 0-6, 9-7.