"Broadway Vitas" Gerulaitis, runner-up to fellow New Yorker John McEnroe in last year's U.S. Open tennis championships, became the tournament's most celebrated casualty to date tonight when he was beaten by Hank Pfister, 6-3, 6-2, 1-6, 7-6, in a second-round match that started with acrimony, ebbed and flowed in quality and built to an excruciatingly dramatic climax.

Pfister, 26, a 6-foot-4-inch Californian who is currently No. 40 in the computerized world rankings, had more than a little bit of luck in the decisive tie breaker, which he won, 8 points to 6, after trailing, 2-4.

Having pulled back to 4-4 in the tie breaker by forcing a lunging backhand volley error with one of his wind-up-and-swing-from-the-hips service returns, and having gotten to 5-5 with a mighty serve on the center line, Pfister reached match point for the first time when Gerulaitis rushed and netted a backhand off a deep but soft volley. "I hit the worst volley in the world, and it floated back into the corner," the jubilant Pfister said afterward. "You've got to get a few of those to beat a guy of his stature."

Pfister blew that first match point, overanxiously blasting a service return four feet beyond the baseline, but Gerulaitis handed him another by pushing an awful backhand volley long. The excitabler Pfister -- by his own description, "really pumped up in the fifth set" -- waved the ball out like a an furiously directing traffice. Then he took several deep breaths, and went back to serve on match point No. 2.

He got his first serve in -- something he had done with little regularity in the match, and escpecially in the last three sets -- and bore in as always for what he hoped would be a killer forehadn first volley.

He drilled the ball, but it clipped the net cord and skipped into the backcourt, sitting up for a clear whack. Gerulaitis -- the No. 5 seed who had lost his serve to trail, 1-2 and 3-4, in the final set, and had broken straight back both times -- went for a backhand, down-the-line passing shot, but knocked it wide.

Pfister, who is not accustomed to winning matches in which he gets only 53 percent of his first serves in, had what he called "the second-biggest win of my life." The biggest, he said, was a 1978 victory over Jimmy Conner in a tournament at Las Vegas in which he also beat Roscoe Tanner and Arthur Ashe.

Gerulaitis, who made the angry and graceless exit-in-a-huff that has become customary when he loses unexpectedly in a big tournament, was the most shocking loser on a day that saw two other men's seeds beaten; No. 8 Eddie Dibbs by Vijay Amritaj, 7-5, 0-6, 4-6, 6-2, 6-1; and No. 9 Peter Fleming by John Kriek, 6-4, 6-2, 6-0.

The other top men who played won with relative ease as the court-level temperature at the sweltering National Tennis Center rose to 116 degrees in the afternoon, then plummeted to a plesant 70 degrees for the night session opened by Pfister's three-hour victory.

Bjorn Borg the five-time French Open and Wimbledon champion who is seeking his first Open title, admitted to feeling tired in the third set of a 7-5, 6-2, 2-6, 6-0 victory over North Carolinian John Sadri, who was aptly desribed by a British writer at courtside as "a man with the mien of a gunslinger in his eyes, and the speed of a bullet in his 138-mile-per-hour serve."

Borg said he felt no ill effects from the sore right knee that caused him so much pretournament concern -- "It's fine, I'm moving well; as long as I don't feel anything, why worry about it?" he shrugged. And he accelerated in the fourth set after Sadri lost his serve from 40-15 in the first and third games. "Those were very important," said Borg. "I think he got a little discouraged."

Borg plays his next match against Peter McNamara under the floodlights he hates on Saturday night, but his coach Lennart Bergelin admitted that if the Swede has to play one night match, as tournament officials insist, this is the one he preferred.

Borg doesn't like playing bullet-servers under lights, and if he beats McNamara, his most likely opponents are both powerful serve-volleyers Yannick Noah and Roscoe Tanner who upset him under lights in last year's quarterfinals.

Tanner today routed 16-year-old Jimmy Arias, the youngest man in the tournament, 6-3, 6-3, 6-0. No. 4 seed Guillermo Vilas -- the only man to beat Borg this year except by default -- now looks like a good bet to reach the semis against him through the quarter of the draw vacated by Fleming, Vitas whipped John Hayes today, 6-2, 6-4, 6-4.

Amritraj, the elegant Indian whose game blows hot and cold, "on" streaks in the final two sets as Dibbs -- a lucky five-set escapee from Bob Lutz in the first round wilted in the oppressive heat and humidity.

Dibbs is from Miami, but Amritraj is even more accustomed to stifling weather. "Vijay plays best in this kind of heat," said brother Anand, eldest of the three tennis-playing Amritraj freres. "This would be just a normal day at home in Madras."

The steamy afternoon may have belonged to Kriek and Amritraj and Tracy Austin -- who trounced Rosie Casals, 6-0, 6-0 -- but the night was the sole property of Pfister. Much of the crowd left after his triumph, not bothering to wait for four-time champion Chris Evert Lloyd to roast and shell Peanut Louie, 6-3, 6-1, in the stadium finale that ran almost to midnight. They had gotten full evening's entertainment and goosebumps from "Hammerin' Hank."