When Chris Evert Lloyd woke up this morning, she was one of the happiest women in New York. And by nightfall, after surviving two hours of extreme three-set aggravation from someone named Bonnie Gadusek, she was even happier.

If anyone at this U.S. Open has gotten the breaks, it's been Evert, who seems on the verge of redeeming what was becoming the most disappointing season of her exalted career.

Tuesday, Martina Navratilova was bounced out of the Open by Pam Shriver, leaving a path clear for the second-seeded Evert to win her country's title for the sixth time in eight years.

Then, before her quarterfinal match against the little-known Gadusek this afternoon, Evert got more good news. Tracy Austin, the No. 3 seed and defending champion, had just joined the top-seeded Navratilova on the sideline, a victim of Hana Mandlikova's slashing strokes.

What a turnabout. Just a week ago, when Evert got food poisoning from a nefarious piece of Flushing Meadow cheesecake, it looked like her luckless '82 season would continue miserably.

Mere prize money means little to Evert. Her tennis life is built around those moments when she holds Wimbledon and U.S. Open trophies over her blond head. Starting in 1974, she has won at least one of her sport's two top championships in every year. Thanks to her food poisoning and Navratilova's 41-match winning streak, Evert looked like a lady about to be shut out.

After such a turnabout in fortune, Evert could have been excused if she were cheerful and complacent as she took the court against the 18-year-old Gadusek this overcast afternoon. An hour later, as Gadusek led Evert by a set and a break -- 6-4, 1-0 -- it was time for Evert to call a meeting with herself.

"I told myself that if I didn't change what I was doing, I'd lose . . . I didn't want to be another casualty," said Evert. "I was being impatient, going for winners on high, deep balls. I have more variety in my game now than I did when I was younger, and sometimes I get overanxious to use it all."

In as elegant a reversal of form as could be imagined, Evert began mixing drop shots and short angled balls with her customary hard base line strokes. Suddenly, the swift, game Gadusek was just a teen-ager in a blue dress and white visor being run to exhaustion by perhaps the greatest woman tennis player in history.

Evert won the last 12 games for a 4-6, 6-1, 6-0 victory that amounted to an adult's punishment of an impertinent youngster.

Gadusek's reward for scaring Evert was that she would be humiliated, not just beaten. "She was like two different people," said Gadusek, a 5-foot-6, 120-pounder from Largo, Fla. "In the first set, she made a ton of (unforced) errors, mostly on her forehand. After that, it was all her. "I've never played in a match that important or in front of a crowd that big," said Gadusek.

Interestingly, Evert used the strongest part of Gadusek's game -- her sheer athletic ability -- to defeat her. When Gadusek was 12, and a promising, perhaps Olympic-quality gymnast, she fell and broke her neck; after six months in a body cast, Gadusek turned her fierce athletic fascination on tennis.

Evert insisted, "I don't have this tournament in the hat." But, in a sense, she does. Her legendary confidence seems intact; in fact, she even admits to disappointment that she couldn't be the one to break Navratilova's streak.

In the end, this day should prove to have been the perfect prep for Evert.

With her patience, her confidence and her luck all in fine form, the rest of the women's portion of this Open may prove to be a piece of cake for her.

But not cheesecake, thank you.