Jimmy Connors, showing little weariness after his loss to Guillermo Vilas in an epic three-hour match that didn't end until 12:42 this morning, defeated Manuel Orantes this afternoon, 6-2, 6-3, to claim the last semifinal berth in the $400,000 Colgate Masters - a tournament that has assumed overtones of theater of the absurd.

Despite his exhausting defeat by Vilas Connors - who finished with a 2-1 record in the round-robin portion of the tournament - suddenly looked like the favorite for the $100,000 top prize as both Vilas and Bjorn Borg defauited their last round-robin matches today.

Vilas, the French, U.S. Open and Grand Prix champion, and Wimbledon champ Borg had already qualified for Saturday's semis of this playoff for the top eight finishers in the 1977 Colgate Grand Prix point standings.

Vilas strained a tendon in his left foot toward the end of his 6-4, 3-6, 7-5 triumph over Connors, that kept a record crowd of 18,590 sweating, screaming and square Garden for an excruciating two hours, 59 mintutes. Surely this must rate as one of the greatest matches of all time, although it was only three sets instead of the traditional championship distance of five.

Borg reportedly was confined to bed with "a severe case of the flu," technically diagnosed as pharangitis. He had a 100-degree temperature and flu symptoms, according to Dr. Norman Rudy, tournament physician and former U.S. Davis Cup team doctor.

Dr. Rudy said there was "a 50-50 chance" for both Borg and Vilas to play in the semifinals, portions of which will bw televised nationally by CBS Saturday afternoon (WROP-TV-9, 3-4:30 p.m.).

Many skeptics considered the odds much better, believing the Vilas and Borg defaults were more a matter of convenience than necessity. These suspicion were reinforced by reports that Borg shot a series of automobile ads for TV and then practiced today, and that Vilas had booked a practice court tonight.

In the Masters format, the top two finishes in each of two round-robin groups advance to the semis, No. 1 of the "Blue Group" playing No. 2 of the "Red Group."

Despite his default to Eddie Dibbs today, Vilas already was assured of being No. 1 in his group because of prior victories over Orantes and Connors. Borg, by subsequently defaulting to Brian Gottfried (3-0), finished 2-1 and second in his group, thus guaranteeing that he would play Vilas in the semi instead of Connors, who now plays Gottfried.

Borg has an 11-4 lifetime record over Vilas. He is 3-7 against Connors.

Borg has beaten Vilas in seven of their last eight meetings, dating back to 1974. Vilas' only victory came in the 1975 Masters at Stockholm, under clouds of suspicion tht Borg might "tank" the match in order to assure meeting Arthur Ashe in the semis rather than Ilie Nastase, against whom he had a much poorer career record.

Tournament referee Dennis Ralston scoffed at suggestion that the players or their coaches - Ion Tiriac (Vilas) and Lennart Bergelin (Borg) - would use a loophole in the tournament format to their advantage, but the possibility remained. "I'm sure the round-robin rules will be carefully re-examined next year," allowed the beleaguered tournament director, Ray Benton of Washington.

Tiriac appeared at a press conference on behalf of Vilas, who he said was at his hotel with his foot elevated. He apologized for disappointing the afternoon crowd of 6,852 spectators, who had paid up to $10 a ticket.

Wojtek Fibak, runner-up to Orantes in last year's Masters at Houston (Borg and Connors did not play), defeated four-times Masters champ Ilie Mastase, 7-6, 7-5, in an exhibition match improvised to fill time before the Connors-Orantes match. Conners won in 1 hours, 23 minutes.

Today's unfortunate events were a distinct letdown after Thursday's rapturous long night's journey into morning. The Vilas-Conners match - their first meeting since the emotion-charfed U.S. Open final four months ago that Vilas won, 2-6, 6-3, 7-6, 6-0 - had even more majesty than that Forest Hills final.

Reaching deep for reserves of iron will that few thought he possessed, Vilas again proved the more rugged streetfighter in a match that ranked second to none for sustained intensity and shotmaking, seeming to defy the laws of physics.

Vilas was on the ropes in the third game of the final set, but held from 15-40 after four deuces and three break points. Starting with the last three points of that game, he won 11 of 13 points of that game, he won 11 take a 4-1 lead.

Then it was Connor's turn to, as he put it, "climb out of the gutter and almost get to the top." He lost only two points in holding serve twice, and broke Vilas from 30-15 when the Argentinian served for the match at 5-3.

At 30-30, Connors blasted a forehand approach off a blistering rally that looked on the line but was called long. Furious, Connors slashed the net with his steel racket, swore, and appealed as the crowd booed.

Hammond intoned "40-30" - match point - and Connors slugged another firehand approach and a two-fisted backhand volley that clipped the net and plopped over for a winner, seemingly vindicating him. Connors pointed at the linesman, frantically yelled "You, you," and then broke as Vilas double-faulted and hit a forehand approach shot inches wide.

Connors promptly held serve for 5-5 and had Vilas looking dazed and tiring at 15-30. But Vilas - winning the 80th of his last 81 tournament matches - held after two deuces in a game that typified the consistently bold shotmaking of both 25-year-old lefthanders.

Vilas' running backhand cross-court winner at 0-30, off a diving Connors volley after both had made impossible "gets," must rank as one of the alltime pressure shots. So, too, must the explosive backhand cross court pass that gave Vilas the games, and a blinding overhead he crunched from the baseline.

Connors led 30-0 in the final game, but missed two forehand volleys to 30-30.Then Vilas detonated another bionic shot, a running backhand down-the-line for an outright winner from the backcourt, to bring him to match point again in this classic close encounter of the best kind.

Vilas - his ankle tender and body and mind drained, but still pumping adrenalin a gallon a minute - danced up and down as Connors served. He looped a forehand return short, and Connors lunged at a high forehand, trying to kill it. He put the ball in the net.

Connors extended his hand, like one prize fighter embracing another after a punishing and captivating bout.

The crowd, largest ever to witness a tournament (non-Davis Cup or exhibition) match, rose and gave both players a thundering ovation for a battle of concussive pace and guts that had enthralled them so long.