Roscoe Tanner, who won the Australian Open in January and was considered a prime title threat in the only other leg of the grand slam played on grass courts became the first major casualty today of the centenary Wimbledon tennis championships.

Tanner, the No. 4 seed who beat Jimmy Connors to reach the semifinals here last year, fell to the sure volleying and backhand service returns of 22-year-old Englishman John Lloyd, 3-6, 6-4, 6-4, 3-6. Tanner, 25, was the only favorite to slip on the slick, rain-deadened turf of the All England Lawn Tennis and Croquet Club.

Defending champion Bjorn Borg defeated Antonio Zugarelli, 6-4, 6-2, 9-7, in the opening match on the spongy green center court. "It's going to be much more difficult than last year to win," Borg said.

Out on Court 13 -- far from the center court where Borg beat Zugarelli, Guillermo Vilas ousted 1973 champ Jan Kodes and Ilie Nastase disposed of Tom Gullikson. Fred McNair IV of Chevy Chase, Md., won the most heroic match of the day, saving four match points to oust California lefthander Nick Saviano, 6-3, 4-6, 6-3, 9-8, 16-14, in 3 hours 37 minutes.

The weather was cold, gray and miserable, another in the succession of dreary days that have left the courts slow; green and slippery. Stewards took blankets to some guests bundled up in the royal box. The ice Iolly hawkers had a depressing afternoon and one matron concluded, "The only way to watch tennis on a day like this is to have two cognacs an hour."

Tanner, known as "the man with aces up his sleeve" because of his leectrifying first serve, won the first 12 points against Lloyd, conceded only one point on serve in the first set, but then seemed to get caught up in the pervasive gloom.

He had been the choice of many knowledgeable people to win the title. Three-time champ John Newcombe, who is having a column ghosted under his byline in a mass circulation London tabloid, picked him. The headline over his piece this morning: "Tanner Will Blitz Then All."

But Lloyd, who had beaten Tanner once, at Los Angeles last fall, had other ideas: "Sometimes I think I've played against names rather than strokes," he said, "so I told myself not to be intimidated. I thought, 'If he serves well, bad luck, but don't beat yourself.'

"He obviously didn't serve as well as he can, but I like to play lefthanders anyway, because they serve to my strength (the backhand). I thought I volleyed well today, because my serve isn't the mightiest weapon ever known. In fact, I occasionally thought I was going to beat it to the net, it was so slow."

"I don't feel like I could put my foot down and push off," said Tanner. "It felt like the foot would squirt out, and sometimes it did. But he still had to make the shots, to put me in that position. He played awfully well and I couldn't get enough first serves in the fourth set."

McNair, in his wonderful little blood-and-guts epic with Saviano, blew one match point at 6-5 in the fourth set and two at 3-7. But he redeemed himself by coming back from triple- match point when Saviano served at 5-3, 40-0 in the fifth, with five clean winners.

"Four return winners and a passing shots. All rifle shots, like I boomed them out of a cannon. I must have been unconscious," exulted McNair, who donned his flared white track suit pants early in the fifth set because he was cramping in his left thigh. He served only at three-quarters pace thereafter because he could not kick off on his delivery, but made the mistake of serving too much twist to Saviano's dangerous forehand.

McNair had another match point against him at 11-12, 30-40 in the fifth. Saviano hit a return at his feet Mc-Nair half-volleyed it and Saviano couldn't decide whether to go for a passing shot or a lob off the ball that sat up in the middle of the court at the service line.

Finaly he lobbed, and McNair summoned a last reservoir of strength to leap just high enough to crunch an overhead. Saviano reflex-volleyed, but the ball went long.

McNair finally broke in the 30th game, after wasting his third match point at 30-40, smashing another overhead just beyond Saviano's lunge on a scrambling point.