Ninth-seeded Eddie Dibbs, playing his patient, baseline game to perfection tonight, upset 1977 champion Guillermo Vilas, 6-3, 5-7, 7-5, 6-1, in the fourth round of the U.S. Open tennis championships.

The match was an endurance test, lasting 3 hours, 7 minutes -- just the kind of match Dibbs likes best. The 5-foot-7 Dibbs, relying primarily on his two-fisted backhand, stayed back and returned everything Vilas shot his way to eliminate the sixth-seeded Argentinian. He is the highest seed to lose in the first seven days of the tournament.

After splitting the first two sets and going to 5-5 in the third, Dibbs took command by winning the next seven games. He held service in a game that went to deuce five times, then broke Vilas' serve at 30 to close out the set.

Vilas, who beat Jimmy Connors in the final of the last U.S. Open before the tournament was moved from Forest Hills to Flushing Meadows, doublefaulted at break point to give Dibbs a 2-0 lead. After that, Dibbs, winner of the year-long Grand Prix points race last season, never let up.

Another upset was averted in the afternoon as four-time Wimbledon champion Bjorn Borg struggled for the first time but managed to defeat Dick Stockton, 6-4, 1-6, 7-6, 7-5, to move into the quarterfinals of the tournament he has never won.

In other matches, fourth-seeded Vitas Gerulaitis, Borg's friend and practice partner, beat 10th-seeded Jose-Luis Clerc, 7-6, 6-2, 6-2, and Johan Kriek outlasted 19-year-old Yannick Noah, 6-3, 7-6, 4-6, 1-6, 6-4, in a battle of unseeded players.

In women's action, Wimbledon champion Martina Navratilova, the No. 2 seed, whipped 10th-seeded Greer Stevens, 6-2, 6-2; No. 4 Virginia Wade advanced when 12th-seeded Regina Marsikova had to pull out of their match in the first game because of torn tendons in her ankle; No. 5 Evonne Goolagong Cawley defeated Jeanne DuVall, 6-3, 3-6, 6-0, and No. 9 Billie Jean King topped Kathy May Teacher, 6-3, 6-0.

Borg, who contends he can't go through a major tournament without teetering on the brink, did just that against Stockton, dropping his service twice in the second set and going down a break in the third before rallying to win the tie breaker, 7-3.

"I'm very happy I survived this match," said Borg, whose next opponent could be Roscoe Tanner, the man he beat in the Wimbledon final. "The difference was only a few points. If he wins the tie breaker, you don't know what's going to happen.

"It was a very tough match. The third set was the most important. After he broke me in the first game I broke him back and that's when I got back in the match. It's the first match I've played against a guy who serves well."

Stockton threw a final scare into Borg by breaking him at love in the 10th game of the fourth set, but the top-seeded Swede responded by winning the next eight points to end the match.