The amateur game, meanwhile, was always sprinkled with screamers and umpire abusers. (If you want to see on-court behavior at its worst today, attend a United States Tennis Association juniors match, a last bastion of amateur tennis, where young players, trusted with making their own line judgments, can be glimpsed “hooking,” or calling their opponents’ shots out even though they are an inch or two in. It happens in N.C.A.A. matches too.) Under-the-table payments from tournament organizers for travel and other expenses were pervasive on the amateur circuit, as players scrambled to make ends meet. Baltzell’s amateur exemplars, Emerson and Stolle, were both employed, in their mid-’60s heyday, plugging brands of cigarettes. “Have one,” Stolle suggested to a Sports Illustrated reporter in the summer of 1964, holding out a flip-top box.

Nor were all of McEnroe’s rivalries embittered. There was Bjorn Borg, whom McEnroe always refers to as his “great” rival, and with whom, on court and off, he was never (or almost never) less than civil. Interestingly, Borg is said to have been a racket thrower as a young teenager. But all traces of any temper were gone by the time he began his rise to the top of the men’s tennis game in the mid-’70s, overtaking Connors and then beginning his competition with McEnroe, which would produce several years of increasingly hard-fought tennis, as they pushed each other’s games with contrasting styles, culminating in 20 or so concentrated minutes of the most galvanizing singles ever played: their fourth-set tiebreaker in the 1980 Wimbledon final. It was a year earlier, indoors in New Orleans, in only their third match against each other as pros (Borg was 22; McEnroe 20), when their relationship as opponents coalesced. They were in the third and deciding set (which McEnroe would eventually win), and it was close. As McEnroe has recounted, “I was getting all worked up and nutty.” At 5-5, Borg had had enough of McEnroe’s antics and motioned him to the net. McEnroe thought Borg was going to berate him. Instead, Borg put his arm around him and said: “It’s O.K. Just relax. It’s O.K. It’s a great match.” It was Johnny Mac’s satori. From then on it was different with Borg. As McEnroe once told an interviewer, “If we could keep lifting our games, I didn’t have to worry about the crowd or the linesmen or anything.”

The notion that a rival raises your game and enhances you somehow in the process is also one Roger Federer came around to, though slowly. He arrived as a young pro at a moment when the Sampras-Agassi rivalry was all but finished, and men’s tennis was unsettled, much as the women’s game is now. Federer won his first Wimbledon championship in 2003 by defeating the big-serving Australian Mark Philippoussis, and as he acknowledged during a press conference at the Sony Ericsson Open in Miami earlier this year — in the most expansive remarks he has made about his rivalry with Nadal — he would have been happy to keep beating players who, whether because of injuries, or lack of commitment, or off-court distractions like, say, Paris Hilton (in Philippoussis’s case, all three and more), came and went quickly in the uppermost ranks of the men’s game. “In the beginning, I guess, I struggled to embrace the rivalry I had with Rafa,” he said. Eventually, though, he saw how it could inspire him and make him play his hardest, and how, as they came to know each other better and enjoy each other’s company, they could work together off the court as the top player representatives of the Association of Tennis Professionals, which oversees the men’s tour, or to help raise money for things like tsunami relief in Japan. What he has with Nadal, he concluded, “is actually quite cool.”

Jimmy Connors is not so sure. He thinks that the sort of rivalry Federer and Nadal have is “soft” and believes that the men’s game could use more of what he and McEnroe had. Nadal, interestingly enough, got to talking about this himself near the end of the first week at Wimbledon. It might have been scripted by Digby Baltzell. “If the kids who are following us see each other fight every week, probably in the future they are going to have the same,” he said. “In my opinion, is not a good way the world have to work.” He continued: “So we can be talking in the locker room before the match — that’s not going to affect what is going to happen in 10 minutes when we are on the court. Probably the opinion of the past champions, they have more troubles between each other. Is different, but for me, the rivalry is only inside the court.”

What ultimately deepens and complicates tennis rivalries — and what makes the game’s manners so necessary as a set of coping mechanisms, if nothing else — is the profound loneliness of the singles game and, for serious competitors, the world around it. To read through the many biographies and autobiographies of renowned tennis players — the only real window we have on the intimacy of tennis rivalries — is to immerse yourself in a literature of not only competition and achievement but also of, most absorbingly, solitude and the self-doubt and lonesomeness it can beget. The lonesomeness, and then the struggle to overcome it in a relationship with the player who is your on-court rival: that, in essence, is the history, or the subconscious history, of high-level tennis.

Of no rivalry is this truer than that of Evert and Navratilova. They had that classic contrast in playing styles: Evert the cool, steady base-liner; Navratilova the ardent attacker, impatient to get to the net. From 1975 to 1987, one of them was No. 1, and for most of those years, the other was No. 2. They shared bagels in the locker room, then took the court against the backdrop of the women’s movement and the nascent gay rights movement, becoming for fans symbols of each — Chrissie, the girl next door who became the woman next door; Martina the out-of-the-closet lesbian. Early on, in 1976, they played Wimbledon as doubles partners and won.

The image that lingers from later, when they fought in all those big finals, was their way of hugging and smiling and even giggling at the net at the end of the match. Even so, Johnette Howard, in her warm and richly reported book “The Rivals,” relates a dream Navratilova had about Evert that those who study rivalries (there are beginning to be researchers who do) might want to consider for a conference panel: “She was playing Evert from a deep valley, and she kept having to scramble uphill, hit a shot, then chase Evert’s return down into the abyss again.”