Sixth-seeded Eddie Dibbs defeated Sandy Mayer, 7-6, 3-6, in a bizarre and eventually acrimonious match last night to advance to the semifinals of the $225,000 U.S. Pro Indoor tennis championships at The Spectrum.

Dibbs seemed to have the 15th-seeded Mayer, conqueror of No. 4 seed Vitus Gerulaitis on Thursday, demoralized when he played a flawless first set tiebreaker and took a 3-0 lead in the second set.

But Mayer, resolutely attacking the net every opportunity, won eight games in a row as Dibbs became inexplicably ragged, to seize a 2-0 lead in the third.

Then Mayer immediately dropped four games in a row, double-faulting to lose his serve to 2-3. It was in the fourth game that the players became embroiled in a long dispute over a line coll at 30-30. A Mayer volley was first called long, then changed. The point was eventually replayed after referee Vic Seixas had replayed lengthy discussions with the umpire, linesman, and both players.

Dibbs won the game for 4-2, lost his serve for 4-1 broke again at love for 5-4 as Mayer drilled an over-eager volley way long, then held from 0-30 for the match.

Ultimately it was Dibbs' passing shots that overcame Mayer's quickness and sometimes acrobatic volleying. But the quality of the shotmaking was as erratic as the pattern of the match.

Third-seeded Brian Gottfried celebrated his 26th birthday by beating John McEnroe, the teen sensation of last year's Wimbledon, 6-1, 6-3.

Gottfried gave himself a present in the first game, breaking the 19-year-old lefthander's serve with a mis-hit forehand passing shot that floated and landed on the baseline. McEnroe, who had hit a pretty good forehand approach, just stood in the forecourt, hands on hips, in scowling disbelief.

Gottfried had gotten to break point by chipping a backhand and coming in behind it for a decisive forehand volley winner, a tactic he used frequently.

The aggressive Gottfried dominated the first set, coming to the net almost at will and grabbing a 4-0 lead. He broke for 3-1 in the second set, immediately lost his serve for the only time in the match, then bore down again for the kill.

Last night's late quarterfinals paired top-seeded Jimmy Connors against Mexican Davis cupper Raul Ramirez and No. 2 seed Bjorn Borg against Rosenoe Tanner.

Borg, 21-year-old Wimbledon champion of the last two years, barely survived a close encounter of the third kind late Thursday night against 6-foot-5 Peter Fleming, whose serves looked liked blurred UFOs.

In a match that capitvated a crowd of just under 10,000, Fleming twice came within two points of victory in the second-set tie breaker before Borg won it, 8 points to 6, and then accelerated to take the match, 3-6, 7-6, 6-3.

Fleming, 23, is one of the most promising young American players, a good-natured UCLA dropout who climbed from No. 116 in the computerized world rankings at the end of 1976 to No. 41 on the new list issued this week.

Slender and angular, with a floppy mop of lank blond hair, he leans into his serve with a mighty crunch and lopes quickly to the net, behind both first and second deliveries, with the gait of an agile giraffe.

When he emcamps himself in the forecourt, his reach seems endless. With his tongue tucked in the corner of his mouth he's a bizarre portrait of determination, lunging side to side. But he leaves little target for passing shots, even for Borg, whose are perhaps the most accurate in the game.

Fleming played a spectacular first set, brushing off the only break point Borg had at 30-40 in the seventh game, then breaking in the next game as Borg double-faulted on the second break point against him, after four deuces.

"A couple of times I've had good players like Dibbs or (Guillermo) Vilas almost beaten, and my heart was pounding so hard I couldn't stand it. It wasn't like that tonight," Fleming said later. It didn't look it as he served out the first set at love, bashing an overhead smash, a clean ace and a forehand first volley winner on the last three points.

The underdog-loving crowd was into the match now, whooping fsor Fleming to push the always icy Borg to the limit, and even more so after Fleming crackled three service winners to hold from 30-40 in the second game of the second set.

Borg started serving better himself, but Fleming hung it grittily, holding from 15-40 in the sixth game and from deuce in the eighth and 10th games. Whenever he needed a big serve he exploded one, and he also was staying with the relentless Borg through long, sizzling, deep rallies, looking for chances to come in but not charging overeagerly.

There were no service breaks in the set, and into the best-of-12-1 points tie breaker they went, the spectators thoroughly absorbed and hanging on every high-velocity point.

Fleming double-faulted to 2-4, and agony was all over his expressive face. He trailed, 3-5, but scrambled back to 5-5 - two points from the match. At that point, Borg admitted later, he thought he might be finished, his hoped for rematch withConnors in the final a prospect dashed.