Wimbledon is a difficult place to come looking to regain your form -- the grass courts eat up pretenders and the crowds are fickle. No. 4 seed Monica Seles found that out the hard way today, losing in the third round to Mirjana Lucic, while No. 3 seed Yevgeny Kafelnikov also left disappointed, withdrawing against Cedric Pioline with a hamstring injury.

Still, if you can figure out the All England club, it can be the ultimate elixir for what ails you. Last year, Pete Sampras used a Wimbledon title to recharge what had been an awful season, and with his third-round win today over Danny Sapsford, 6-3, 6-4, 7-5, he appears to be on the path to rejuvenation once again. Jim Courier, who fell to No. 118 last year, continued his march back into the top 50 by winning a five-set thriller. And John McEnroe, who last played singles here in 1992, stepped back onto the green lawns to rousing applause when he and Steffi Graf won their long-awaited mixed doubles match.

"I was nervous and excited -- I just wanted to hold up my end of the bargain," said McEnroe, who won three singles and five doubles titles here. "There are a lot of ebbs and flows and ups and downs in sports, but I was looking forward to this from the moment we decided to do it, and I tried not to stink, basically."

Graf looked like she was having just as much fun as McEnroe, matching her 40-year-old partner gesture for gesture to entertain the crowd. When she hit the first point of the match wide, McEnroe faked anger, dropping his racket and sulking. When McEnroe hit the following point into the net, Graf dropped her racket, putting her hands on her hips. The fans exploded into laughter, and even McEnroe and Graf's opponents, Jeff Coetzee and Eva Meli'rova, seemed amused, taking a pleasantly resigned attitude as they lost, 6-2, 6-4.

The spirited display capped a busy day for Graf, who also won her singles match against Corina Morariu to join Venus Williams and Anna Kournikova in the fourth round. Because of Amanda Coetzer's loss to Dutch teenager Kim Clijsters today, Graf will have a relatively inexperienced opponent, but Williams and Kournikova will face each other in a match that is sure to be highly charged and well-photographed. The sixth-seeded Williams had been on course to play her sister Serena in the fourth round, but Serena defaulted before the tournament began and Kournikova slipped into her position in the draw.

"It's going to be a tough match," said Kournikova, who was given a 17th seed. "Venus has a big serve and she's a big girl, so I just have to out-think her and try to play my game, because grass is obviously not one of her favorite surfaces. So we'll see. I just have to try to play smarter."

Williams said later that she has no problem playing on grass, an assertion she backed up with a 6-1, 6-1 drubbing of Sarah Pitowski. Nothing came that easily for Seles, who fell to the 17-year old Lucic, 7-6 (7-4), 7-6 (7-4).

This is the one Grand Slam that Seles has never won, and while she reached the finals in 1992, she has never looked comfortable on the lush lawns. She had hoped things would be different this time, as she has not been to a Grand Slam final in more than a year and has not won a Slam title since claiming the Australian Open in 1996. But despite starting today strong on serve, allowing Lucic just one point over her first six service games, she struggled on Lucic's serve, especially in the tiebreakers.

"It was weird," Seles said. "I had a few chances, but my returns were nowhere, and as the match went along, they just disappeared. I didn't get too many chances to get into the match in my mind."

Courier had a much different kind of struggle on his hands in a 7-6 (7-2), 3-6, 3-6, 7-5, 13-11 victory over Sjeng Schalken that left him dehydrated and needing intravenous fluids. Courier fended off two match points, the first coming when he was down 4-5 in the fourth set. He hit a pinpoint forehand passing shot to stave off elimination, but he found himself threatened again at 5-6 in the final set. That time, a scorching backhand saved him.

By 23rd game of the fifth set, Schalken looked worn, double-faulting twice, and Courier was able to win the match when he held serve at love. The victory earned Courier his first fourth-round appearance since the 1997 Australian Open; he has been spending this year trying to rebound from an arm injury that plagued him last year.

"That's Jim's strongest quality, his heart," Sampras said just moments after Courier finally closed his match. "He's going to lay it on the line and fight to the last point, and you know, today was a perfect example of that. I know he has struggled a little in the last couple of years with his tennis and his injuries, and it's good to see him playing well."

WIMBLEDON 1999

When: Through July 4.

Where: All England club, Wimbledon.

Defending champions: Pete Sampras, Jana Novotna.

Top seeds: Sampras, Martina Hingis.

Today's TV: 1 p.m., WRC-4, WBAL-11.

Yesterday's results: Men -- Pete Sampras (1), United States, def. Danny Sapsford, Britain, 6-3, 6-4, 7-5; Cedric Pioline, France, def. Yevgeny Kafelnikov (3), Russia, 3-6, 6-4, 1-0, retired; Tim Henman (6), Britain, def. Sebastien Grosjean, France, 6-1, 6-7 (8-10), 6-3, 6-2; Jim Courier, United States, def. Sjeng Schalken, Netherlands, 7-6 (7-2), 3-6, 3-6, 7-5, 13-11; Daniel Nestor, Canada, def. Paul Goldstein, United States, 6-3, 6-7 (3-7), 6-0, 6-7 (4-7), 6-4. Women -- Steffi Graf (2), Germany, def. Corina Morariu, United States, 6-1, 6-3; Mirjana Lucic, Croatia, def. Monica Seles (4), United States, 7-6 (7-4), 7-6 (7-4); Venus Williams (6), United States, def. Sarah Pitkowski, France, 6-1, 6-1; Kim Clijsters, Belgium, def. Amanda Coetzer (12), South Africa, 6-2, 6-4; Anna Kournikova (17), Russia, def. Ines Gorrochategui, Argentina, 7-5, 3-1, retired.

Today's featured matches: Men -- Boris Becker, Germany, vs. Lleyton Hewitt, Australia; Thomas Enqvist, Sweden, vs. Patrick Rafter (2), Australia; Alberto Martin, Spain, vs. Andre Agassi (4), United States; Richard Krajicek (5), Netherlands, vs. Lorenzo Manta, Switzerland. Women -- Lindsay Davenport (3), United States, vs. Laura Golarsa, Italy; Maria Antonia Sanchez Lorenzo, Spain, vs. Jana Novotna (5), Czech Republic; Elena Wagner, Germany, vs. Mary Pierce (9), France; Jelena Dokic, Australia, vs. Anne Kremer, Luxembourg; Conchita Martinez, Spain, vs. Lisa Raymond, United States.

CAPTION: Steffi Graf, John McEnroe win mixed doubles match, 6-2, 6-4. "I tried not to stink," said 40-year-old McEnroe.

CAPTION: In third-round match, Mirjana Lucic of Croatia, above, sends Monica Seles packing, 7-6 (7-4), 7-6 (7-4).