John McEnroe and Tim Mayotte exited the Sovran Bank Classic yesterday with similar gasps for air and whimpers that have become too familiar of late, their attempts to return to the top of the tennis hierarchy thwarted at least temporarily. Meanwhile, the remainder of the tournament's top seeds advanced to the quarterfinals with relative ease at the William H.G. FitzGerald Tennis Center in Rock Creek Park.

On a day that saw victories by Andre Agassi, Brad Gilbert and Michael Chang, Derrick Rostagno followed his straight-set win over McEnroe at Wimbledon last month with another victory over the former No. 1 player, this time with a 6-3, 1-6, 6-1 decision in a third-round match that produced the week's best tennis and most tense moments.

With 7,500 -- plus those standing in the aisles -- of the tournament-record 8,500 looking on at the Stadium Court, 113th-ranked Rostagno buried third-seeded McEnroe beneath an onslaught of serve-and-volley tennis.

He overpowered McEnroe, ranked 12th and beginning his latest declared recommitment to the game, in rushing to a 3-0 first-set lead. He survived a lull late in that set and throughout the second, then renewed his blitz en route to a 5-0 advantage in the third.

"I just don't have enough ammunition at this time to hurt him," said McEnroe, composed but somber in his postmatch news conference. "He was just too good on this day."

Earlier, Mayotte -- the defending champion and fourth seed -- was beaten by Todd Witsken, 2-6, 6-4, 7-5, after serving for the match at 5-3 in the final set. But Witsken, seeded 14th, won the final four games to extend Mayotte's recent slide and set up a first-ever matchup with fifth-seeded Chang.

"I don't think I've ever lost a match where I had so many chances to win," said Mayotte, who also blew a 4-2 lead in the second set before destructing amid a flurry of botched volleys, erred ground strokes and double faults.

The McEnroe-Rostagno match had the atmosphere of a Grand Slam event. It was Rostagno who raised his game, though, during a first set in which McEnroe complained often about line calls. Rostagno controlled the play, with McEnroe reviving to save four set points before Rostagno won it on the fifth chance with a lunging cross-court winner off a testing McEnroe return.

McEnroe's second-set runaway was partly the product of Rostagno's game leveling off and partly attributable to McEnroe's progressing. He cut his mistakes and broke Rostagno twice for a 5-0 lead before serving out the set.

But the decisive set was all Rostagno's. He rallied from 0-30 with three straight backhand winners in the second game, then broke with a backhand drop shot for a 2-0 lead. McEnroe was sagging and Rostagno surging, and the result never was in question.

"Any time you lose, it's disappointing," said McEnroe, who vowed to continue his attempt to recapture past brilliance. "That's the tough part of losing -- overcoming the disappointment. The hurt of losing, as you get older, is more than the excitement of winning."

Rostagno is the tour's leading free spirit, an engaging 24-year-old who once maintained vans on both coasts. Asked to compare the win to his Wimbledon triumph, he replied, "They were both three sets."

It has been a year of injuries and disappointing showings for Mayotte. He missed three months with a bad right knee, and pledged upon his return to undertake a fine-tuning of his game.

But the results have been disastrous, with a first-round loss at Wimbledon and second-round loss last week in Newport, R.I. He said he often slips "into a limbo" between his old style and new, and such indecision combined with fatigue to produce his collapse yesterday.

He netted a simple volley while serving at 4-2 in the second set to help Witsken get back into contention, and was broken four times in the final set. Mayotte could manage only a single point in each of his final two service games.

"I could definitely tell he was getting tired," said Witsken, who lost to Mayotte in the semifinals here last year. "I'm in pretty good shape, so I knew it was to my advantage as things went along."

Top-seeded Agassi survived a second-set scare to top Gilad Bloom, 6-1, 7-5, in the night's final match. The 15th seed had a 4-0 lead before apparently losing his intensity while Agassi began some clowning antics. The neon-clad 20-year-old increased the power behind his stinging ground strokes, and Bloom couldn't keep pace.

In the quarterfinals Agassi faces seventh-seeded Richey Reneberg, a tough 24-year-old who is ranked 39th and also owns a victory over McEnroe this year. He outlasted Darren Cahill yesterday, 6-4, 2-6, 7-5, overcoming an early break in the third set and benefiting from a dubiously timed foot fault on Cahill at deuce in the final game.

Chang wasted little time with Simon Youl, dispatching the Australian in 56 minutes with a 6-1, 6-1 pasting. He seemed to capture every key point and never was seriously threatened, moving into the quarterfinals with the hope of breaking a string of summertime disappointments.

"I didn't get past the quarters of any tournaments last summer," said Chang, who had hoped for a rematch with Mayotte, his conquerer at both Wimbledon and the U.S. Open in 1989. "I'm kind of stuck on that quarters mark for some reason. I'm kind of sick of the quarters. . . . I hope I can make myself step up into the half-dollars area."

Gilbert, the second seed and last year's runner-up, had few problems with 16th-seeded Andrew Sznajder in a 6-2, 6-3 victory. But the No. 6 player in the world said he fears some inconsistencies in his game that have showed in his two wins this week may haunt him in later rounds.

He was broken by Eliot Teltscher while serving for the match in his second-round victory Tuesday, and he suffered from some faulty shot making that allowed Sznajder to get back into the second set with a break at 2-4.

"I played really well overall, but there was that one loose game at 4-2," Gilbert said. "I've been doing that a lot. I let up for a game here and there. Maybe if I play someone who's a little higher ranked, he might take advantage of that a little better."

Sznajder certainly didn't utilize his opportunity, permitting Gilbert to break back immediately for a 5-3 lead and close out the match with his next service game. The summer hard-court season traditionally is the time of the year to which Gilbert looks forward, and he has begun to craft a solid 1990 already -- with two wins and a quarterfinal showing at Wimbledon, at which he lost to Boris Becker.

And he probably is relieved that his quarterfinal opponent here won't be 10th-seeded Jakob Hlasek, a hard hitter who lost yesterday to doubles partner Michael Stich. Stich, who also upset eighth-seeded Alexander Volkov Tuesday, prevailed, 7-6 (7-5), 7-6 (7-4).

Sixth-seeded Jim Grabb defeated Grant Connell, 6-4, 6-4, in an afternoon match and was looking forward to a potential first meeting with McEnroe. Of course, he also had cause to pull for Rostagno, a former teammate at Stanford.