Ivan Lendl and any ticket-holder hoping to see him play later in the week received a major scare at the Sovran Bank/D.C. National Tennis Classic yesterday at Rock Creek Tennis Center.

But David Wheaton, an 18-year-old Stanford freshman-to-be, couldn't maintain his one-set lead, and Lendl came back to win, 6-7 (7-5), 6-3, 6-2, in a 2-hour 29-minute match to advance to the quarterfinal round. Lendl later defaulted a scheduled doubles match because of heat exhaustion but is expected to resume play Friday.

When Wheaton, ranked 428th in the world, won the first-set tie breaker, the sellout crowd of 5,500 at the stadium court was unsure whether to cheer for the underdog or face losing the tourney's top seed.

But trailing, 2-1, in the second set, Lendl won nine of the next 10 games. When the smoke cleared, he was up by 4-0 in the third. "I didn't stay with him in the second set. He started playing too good," Wheaton said.

And Boris Becker showed the crowd that he is still Boris Becker with a crisp, 6-4, 6-2 victory over John Ross.

Becker, the No. 2 seed, said he felt tired in his first match, but there was no sign of sluggishness last night. "He seemed like he was pretty fit to me," said Ross, a trifle wryly.

Third seed Jimmy Connors easily ousted No. 14 Jim Pugh, 6-3, 6-1, in a match that lacked the drama of Lendl-Wheaton.

Marty Davis provided the upset of the day, knocking off No. 5 Johan Kriek, 6-4, 7-6 (7-4). That set up a quarterfinal match with No. 4 Brad Gilbert, who moved past No. 13 Nduka Odizor, 6-4, 6-4.

Lendl will face No. 7 Jimmy Arias, who advanced with a 7-6 (8-6), 6-3 victory over Simon Youl of Australia. Eighth-seeded Jay Berger had no trouble with Blaine Willenborg, 6-1, 6-2, and next faces Becker. Todd Witsken, the 12th seed, set up a meeting with Connors with a 6-0, 6-1 victory over Laurie Warder of Australia.

Connors broke Pugh in the seventh and ninth games of the first set. In the fourth game of the second set, with Connors up, 2-1, Pugh could only send defensive lobs at Connors and fell behind, 15-40, when he netted Connors' overhead. He then missed on a crosscourt shot to give Connors a 3-1 advantage.

Connors held for 4-1, then broke again for 5-1. He closed out the match at love.

Connors said his improved play this year is the result of a book published last year. "I wrote a book on how to play tougher tennis. And I read it," he said, adding the book brought him back to the basics that allow him "to play the kind of tennis that's expected of me."

In the opening match, Wheaton conceded, "In the first set I went out there thinking I had nothing to lose, really."

With the tie breaker at 5-all, Lendl went to the net after a long base-line rally. Wheaton sliced down the line. Lendl half-volleyed, but Wheaton came up and sent a backhand down the line that Lendl couldn't handle for a 6-5 lead. Wheaton then came behind his serve and put away an easy half-volley to take the set.

Wheaton broke in game three of set two, but Lendl used a crosscourt forehand winner and a backhand down the line that Wheaton barely touched to break back and tie the set at 2.

After holding for a 3-2 lead, Lendl broke for 4-2 when Wheaton netted a backhand approach. Lendl held for 5-2, and Wheaton saved set point with a service winner for 5-3. But Lendl hit a service winner at 30-all and Wheaton netted a backhand to give Lendl the second set.

Wheaton's last gasp came with Lendl up 4-1 in the third set, when he forced six deuces before Lendl held serve.

"At 4-1, he started getting real tired," Wheaton said. "I knew he wasn't going to use up all his energy to break me. But you saw how long it took him to get tired . . . you can see that he's ready to play five sets."

But Lendl and his doubles partner Bill Scanlon defaulted their second-round doubles match to Chip Hooper and Gary Muller because of heat exhaustion Lendl suffered in the first match.

Becker's victory over Ross was much less tiring.

Ross stayed with Becker to 4-4 in the first set. "Then he gave me a little different look," said Ross. "That's something you expect from a great player. I started going for a little bit too much. . . . Playing somebody like that -- sure, you press a little bit."

Becker said that it wasn't so much his having a different look as his getting used to Ross'. "He doesn't give you much of a rhythm, so it took a while to get into it, to know how to break him," said Becker. When he got the rhythm, "then I picked it {level of his game} up. . . . I started hitting more returns {of serve} back, being more aggressive. That's more pressure to him."

Becker closed out the first set with two love games, then won the first four games of the second set. Ross had three break points in the fourth game of the set, but Becker dug himself out of a 15-40 hole with an ace and a service winner, then, after another break point and four deuces, finished the game with a service winner.

Ross got a break back in the sixth game to close to 4-2, but Becker broke right back and served out the match at 15.

Gilbert broke Odizor in the third game of the second set aided by passing shots -- one forehand and one backhand -- set up by blocking returns off strong Odizor serves. That gave Gilbert a 2-1 lead.

The match remained on serve the rest of the way with Gilbert advancing by serving out at 15.

Davis pulled the upset with a strong serve-and-volley game -- and some errors by Kriek.

"I played {terrible} and he played great," said Kriek. "I never could make contact with the ball, I never felt good hitting anything. When it doesn't go, it doesn't go."

With the second-set tie breaker tied at 3-3, Kriek netted a backhand, was long on a backhand return of serve and watched Davis' backhand volley off a net cord streak past him. That gave Davis a 6-3 edge. He netted a backhand return, then finished the match with a forehand crosscourt return of serve for a winner.