From Hard courts: real life on the professional tennis tours, by John Feinstein:

Arantxa Sanchez had been having an inconsistent year, and few people gave her much chance to defend her title. But even fewer people thought that Mercedes Paz, her doubles partner, would be the person to knock her out of the tournament.

Paz was a month shy of twenty-four and had been on tour for six years. People said she could really be a factor if she ever got in shape, but at the end of 1989 she weighed 184 pounds. Even at five feet ten, that was a lot of weight to be carrying. She had finally gotten herself on a training regimen at the start of the year and had lost twenty-five pounds. She was still bulky and lacked quickness, but the difference in her game was evident.

Sanchez, meanwhile, was going through a difficult time. She had changed coaches earlier in the year, hiring Mike Estep to replace her longtime coach, Juan Nunez. Estep had a simple philosophy when it came to coaching women: anybody can attack if they want to; he had made Martina Navratilova more aggressive when he began coaching her in 1983, getting her to come in behind her second serve, and he had preached the same kind of game to every player he had worked since then.
At forty-one, Estep was thinking it might be time to get off the tennis merry-go-round. But IMG had called to say Sanchez was looking for a coach. They were willing to meet Estep’s financial terms – which included first-class airfare for him and his wife Barbara – and wanted him to meet with Sanchez. he did, liked her and her family, and took the job. Right now, though, Sanchez was caught in the middle. Part of her understood why Estep wanted her to be more aggressive, but a major part of her still felt more comfortable hugging the baseline. An indecisive player is almost always a losing player.

“What you can say?” Sanchez said in her fractured English after the match. “Last year I win there; this year, I don’t. It happens.”

She was exactly right. What Sanchez had done in 1989 was extraordinary. The problem was, in tennis, everyone demanded that the extraordinary be repeated over and over again.

Extract from The Rivals by Johnette Howard:

“By the late-August start of the 1983 US Open, Navratilova had won all five of her 1983 encounters with Evert, and eight of their last nine matches overall. The US Open still loomed as the last major title Navratilova had never won despite ten previous tries. If Navratilova was going to finally win the tournament, it seemed only fitting that she found herself having to go through evert for the championship. As the two of them padded around the otherwise deserted dressing room the day of their final, staking out their own corners and quietly preparing themselves to play, they both knew they were at a crossroads.

Navratilova and Evert were about to play the thirty-ninth final of their decade-long rivalry, and their record now stood at perfect equipoise: a 19-19 deadlock in championship matches. After so many years spent chasing Evert, Navratilova would finally, inarguably nudge ahead with a win. It would be the last accomplishment Navratilova needed to signify that she had finally conquered herself as well as Evert.
As Navratilova waited to take the court, her legs began to shake. Her hands were trembling. She told Mike Estep:

The time is now. It’s now or never.

Navratilova took the first set from Evert so quickly, a skywriting plane that was droning high over the stadium was unable to finish writing “Good luck Chrissie” until three games were already done in the second set.
Nothing hindered Navratilova – not the 93 degree heat, not her pre-match nerves, not her awful history at the Open. She overwhelmed Evert 6-1 6-3, in just 63 minutes. She celebrated match point as if a jolt went through her body. She flung both her arms in the air. Her eyelids snapped up like two window blinds that had been rugged down and let go. Her mouth opened wide and she screamed.

If I don’t win another tournament in my life, at least I can say I did it all.

Navratilova’s performance was so complete, there was little Evert could do beyond affectionately tap Navratilova on the head with her racket and smile when they shook hands at net, same as she had done the first time Navratilova finally won Wimbledon five years earlier.”