Pam Shriver had to play only three games to win her first-round singles match against Heidi Eisterlehner today, but it wasn't easy. She had been playing them in her mind for about 18 hours, and she was mentally exhausted.

The match was suspended by darkness at 9 o'clock Wednesday evening with Shriver leading, 6-4, 3-6, 3-1. She closed it out with three games in a row, but only after saving a break point in the first game with a back-hand volley. An important volley, since she had gone on court with her nerves frayed and her heart pounding like a base drum.

"I've never had a match held overnight before," said Shriver, the 6-foot, 140-pound pride of Lutherville, Md. "It's kind of hard, because you don't sleep to well or anything.

"All night long, I thought about that first game, and told myself, 'You've got to hold serve.' I swear, I woke up and looked at my watch and thought it was at least 7 in the morning. It was 2:30. I didn't sleep much after that.

"I was real nervous going out there. Did you see the first game?"

It looked as if she was hyperventilating, she was told.

"Close," she said.

She was practicing so hard, someone commented, that her anxiety was painfully apparent even in the top row of the 1,450-seat grandstand on Court 13, in the far corner of the congested All England Lawn Tennis and Croquet Club grounds.

"Yeah, because I knew that if I held my serve the first game and got to 4-1, I'd be fine. But if I had lost if for 3-2, gosh, I don't know what would have happened," she said.

It has been an unpredictable, emotion-jarring and rather trying year for Shriver, who became in September 1978, at age 16, the youngest finalist in the history of the U.S. Open.

Suddenly, she was in international celebrity -- nicknamed "The Great Whooping Crane" because she was a tall, stork-like kid with a baby face and a very grownup game -- an explosive, demonstrative net-rusher who pounded mighty serves, volleys and smashes with her oversized Prince racket.

Although she won't turn 18 for another eight days, on the Fourth of July, Shiver has been through a life-time of emotions since that giddy late summer vacation's dream two years ago.

First, she struggled through a combined junior-senior year at the demanding McDonogh School near Baltimore, which didn't leave much time for tennis.

Then, after graduation last June, she came to England and suffered a shoulder injury, which lingered the rest of the year, and clouded a future that had seemed unquenchably bright.

Shriver had to default after winning one match at Wimbleton last year, and has been battling desperately ever since to fulfill the promise that had beckoned so tantalizingly in the autumn of '78.

Last summer, she was a first-round loser more often than not. She bottomed out in the U.S. Open, where she lost in the first round to qualifier Julie Harrington.

Shriver left that match in tears. Her shoulder arched. She knew it was time to start over. A specialist prescribed an arduous series of exercises to build the shoulder to a strength that could withstand the considerable strain of the big serve she once had taken for granted.

It has been a long and winding road since then. There have been encouraging patches, glimpses of grandeur, along with disappointing regressions. She has practiced hard, gritted her teeth and sweated through countless painful sessions with weight machines to rehabilitate the shoulder. But the results on the court have been maddenly erratic.

The progress has been decidedly gradual. From her lowest ranking, No. 36 in the Women's Tennis Association computer in late January, she has climbed back to No. 21.

She reached the quarterfinals of two Avon tour tournaments (Kansas City and Dallas) last winter, and in March won a minor tournament in Carisbad, Calif. After saving two match points against Barbara Hallquist in the first round, she beat Kay McDaniel, Terry Holladay, Stacy Margolin and Kate Latham to win the $8,500 first prize.

"They're not the cream of the crop, but darn, they're all in there around the 20s in the rankings, and I went right through them," Shriver said today.

"I haven't played that well against the top players yet, but that was the high point. I was feeling and playing great.I haven't played quite as well in a tournament since then, but I know it's only an inch away. I guess that's enough to keep you going. Knowing something is that close, you want to find it."

Her coach and confidant -- the Australian-transplanted-to-Baltimore, Don Candy -- has told her repeatedly that it will be a slow trek to the summit, that she must not let her dreams exceed her means.

"Don is very careful.He tells me to take small steps and not expect things too quickly," she said. "I think that maybe my main problem: things happened in such a hurry in 1978. I thought, "Well, it's sort of mapped out for me. Here it goes.

"But, boy, the reality is nothing like that, especially when you're the type person that I am -- kind of emotional and a little up-and-down. I think you have to be patient, because where I want to be is a couple of years off, for sure. If I get there, that is. So why be impatient now?"

Well, because Tracy Austin -- the age-group rival who Shriver never has beaten -- won the U.S. Open in September at 17, and is seeded No. 2 in this Wimbledon, expected by many to win.

And because Andrea Jaeger, at 15, also is seeded here -- and confident enough in her skills and effortless style of play to stay after her first-round match:

"I think it's a lot different for me than for the other players, because some of the others get here and go. 'Oh, there is my biggest thrill, to make Wimbledon.' And then some of them say, 'Oh, I want to win Wimbledon.' But when you're my age and you get in Wimbledon and get seeded at Wimbledon, there's not much more that you can want other than to win Wimbledon."