It was like the first day of school. Everyone was a little bit nervous after such a long vacation -- "Good nervous, not bad nervous," said Martina Navratilova, last year's top pupil. But despite the jitters, by the end of the day, the best students were back where they belonged -- at the head of the class.

The first-round matches in the 1981 Colgate Series Championships -- the tournament that supposedly decides No. 1 for 1980 -- were played yesterday at Capital Centre. When they were over, all the women with a legitimate chance to come out of the $250,000 event with the $75,000 first prize were 1-0.

In the afternoon matches, fifth-seeded Martina Navratilova defeated Wendy Turnbull, 6-2, 6-4, and third-seeded Tracy Austin defeated Virginia Ruzici, 6-0, 6-3.

In the evening, top-seeded Hana Mandlikova beat 15-year-old Andrea Jaeger, 7-5, 6-3, and Chris Evert Lloyd beat Pam Shriver of Lutherville, Md., 7-5, 6-3.

In second-round matches today, Ruzici meets Jaeger and Turnball plays Shriver in the afternoon. Tonight, Mandlikova will try to beat Austin for the first time (she is 0-5). And Navratilova will play Evert for the 41st time. Evert is 27-13 against Navratilova (they are 2-2 in 1980).

Most of the players in the tournament have been off for the last month -- in Evert's case, two months -- and it showed in some early-round raggedness.Austin, who played most recently, winning the Tucson Open in December, looked the sharpest in defeating sixth-seeded Ruzici, 6-0, 6-4. Austin won the first 10 games, and Ruzici was as helpless as Austin was flawless.

Ruzici lunged at the pinpoint groundstrokes Austin launched from the baseline, mostly to her backhand. She looked like the pendulum on a grandfather clock as Austin moved her back and forth across the court, chasing groundstrokes that hugged the baseline.

"Until it was 6-0, 4-0, she made only two mistakes. . . I counted," Ruzici said.

The Evert-Shriver match was almost as one-sided. Shriver, who said she was uptight playing before a number of hometown fans, started off with a bang, two aces in the first game. But soon her game began to whimper. Evert broke her serve in the third game as Shriver made three errors and lost the game on a double fault. It was the only break of the set.

Evert broke Shriver's serve again, in the first game of the second set, as Shriver, who was mis-hitting volleys, and sailing shots long and wide, again double-faulted to lose the game.

Jaeger and Mandlikova, neither of whom have played in this tournament before, played the finest tennis of the first day. But they, too, started off rocky, as Mandlikova double-faulted three times in the first game, and Jaeger went up a service break.

But the quality of play picked up after that, with Mandlikova displaying some fine shotmaking, wonderful backhand volleys and forehand winners. She also served seven aces. At 30-15 in the seventh game, Mandlikova hit a backhand drop shot which brought Jaeger to the net, and then ended the point with a forehand volley. She broke Jaeger with a running cross-court forehand, to tie at 3-3.

Mandlikova won the set by breaking Jaeger again at 6-5. Jaeger saved one set point, when Mandlikova sailed a backhand long, but lost the set, finally, when Mandlikova hit a backhand cross-court volley beyond her reach.

In the second set, the players exchanged breaks three straight times. Mandlikova broke first to make it 4-2, then Jaeger made it 4-3. In the eighth game, Mandlikova, who was moving in and teeing off on Jaeger's second serve, hit three forehand winners to go up, 5-3.

Jaeger said, "If she gets her serve in, it's hard to do anything with it. You make a couple of mistakes on your serve, and you've lost it."

For Navratilova, the 1980 Colgate champion, the year was a year of wondering whether she had lost it. Navratilova, who did not win a major outdoor title in 1980, has lost only one match here in the last six years. Some people call this surface Sporteze. She calls it a magic carpet.

She seemed pleased with the ride it had given her in beating Turnbull, who beat her twice last fall. "I hit some shots that I haven't hit in a long time," she said. "I had one pickup half-volley that was a flash from last year. Maybe this place is magical. I really did play much better than I have been playing."

The flash came at 1-1 in the first set. Turnbull, who has been having trouble with her serve and with making the adjustment from playing outdoors to indoors, missed her first serve at 0-15. Navratilova charged the net on the second serve. She made one volley, and pirouetted 360 degrees just in time to make a backhand pickup half-volley that she deposited out of Turnbull's reach.

"It only gave me 0-30," Navratilova said, who went on to win the game, the set and the match. "But it made me feel I could do anything."

That feeling may have been the most significant development of the first day of play.