INGLEWOOD, Calif. &ndash; God-like creatures that they were, at least to New York baseball fans, Mickey Mantle and Willie Mays faced off in only one World Series during their careers in the city, in 1951, when both were rookies. As showdowns go, it was hardly the stuff of drama. The Yankees won in six. Mays had four hits for the Giants, and Mantle blew his knee chasing a fly ball hit by Mays part way through Game 2.\r\nThough 10 years apart in age, Arnold Palmer and Jack Nicklaus gave golf fans a great ride in the 1960s, accounting for 13 of the 32 &ldquo;majors&rdquo; played between 1960 and 1967. In five of those 13, Palmer and Nicklaus finished one-two. Now that&rsquo;s how a rivalry is supposed to work.\r\nThen there was Wilt and Kareem, one of the greatest basketball rivalries between big men in the history of the sport, played out over the four remarkable seasons at the end of one career and the beginning of the other. Over a stretch of 28 games, the younger Jabbar outscored Chamberlain, and Chamberlain outrebounded Jabbar as their Bucks and Lakers split the difference, 14-14.\r\nSuch great matchups provide the defining elements of a sport, even more than the skill of play or the records compiled by the ever-changing composition of teams. Fans prefer their passions to be focused and distilled as often and as intensely as possible, which is why there are so many reasons to be thankful for Jimmy Connors vs. Bjorn Borg, Don Drysdale vs. Henry Aaron, Mario Andretti vs. A.J. Foyt, Peyton Manning vs. Tom Brady.\r\nHorse racing has donated its share of rivalries, in a tradition embodied by Kelso and Gun Bow, Dr. Fager and Damascus, Affirmed and Alydar, Sunday Silence and Easy Goer. When they took the field, time stopped and the rest of the cast faded from view. Each of the rivals served to define the other in everlasting terms.\r\nRachel Alexandra and Zenyatta could have provided such a rivalry, perhaps, if the stars and the races and the various agendas involved had more advantageously aligned. They had geography working against them, to be sure, as well as a two-year age difference that allowed for the younger Rachel to play out a challenging string against her contemporaries.\r\nAs a result, Rachel Alexandra compiled what was probably the best single season ever for a 3-year-old filly in 2009, during which she won all eight of her starts, two of them classics, and defeated males on three separate occasions. As a bonus, Rachel Alexandra&rsquo;s appearances lent support to a whirlwind of promotional activities, elevating her profile into the wider sporting world and taking horse racing along for the ride.\r\nFor her hard work, Rachel Alexandra was crowned Horse of the Year. But there was a cost. In losing three of her five races this year, never without a fight, she proved once again that a great 3-year-old may turn out to be merely a good 4-year-old, and that among top horses of a certain age, even the slightest flinch will be exposed.\r\nIn truth, the only race of Rachel Alexandra&rsquo;s for which Zenyatta was eligible during the 2009 season was the Woodward Stakes at Saratoga, against older males. Zenyatta&rsquo;s people, as it turned out, had bigger fish to catch in the Breeder&rsquo;s Cup Classic down the line. And so the moment passed.\r\nGiven that Rachel Alexandra&rsquo;s 2010 was something less, by her lofty standards, and that Zenyatta&rsquo;s has been a continuation of a steady theme based on home cooking, the idea of a true rivalry never gathered much steam, beyond the sometimes heated conversations among fans.\r\nTrue, there were pronouncements from both owners, Jess Jackson and Jerry Moss, that they would love nothing more than a showdown. Occasionally their trainers, Steve Asmussen and John Shirreffs, would weigh in with nice things to say about the other man&rsquo;s mare. But when Rachel Alexandra stayed home in New Orleans last March, giving Zenyatta a free pass in the Apple Blossom at Oaklawn, the writing on the wall became painfully clear. Chances they would meet were boiling down to slim and none, and there were no independent brokers stepping forward to make the impossible happen.\r\nThis is the cold reality. Horse racing, bless its chaotic, seat-of-the-pants soul, has no framework to nurture great rivalries, unless you count the brief window afforded by the Triple Crown. Even then, the more recent trend is for the also-rans to head down the road and plan backward from the Breeders&rsquo; Cup. Or early retirement.\r\nWith unbeaten Zenyatta on target for her 19th win in the Lady&rsquo;s Secret at Hollywood Park on Saturday, had Rachel Alexandra answered the call for the Beldame the same day at Belmont Park &ndash; instead of being retired &ndash; it would have marked the third time they would have shared the national stage, in remove.\r\nOn June 27, 2009, a half-hour before Zenyatta won her second Vanity Handicap at Hollywood Park, Rachel Alexandra took apart the Mother Goose at Belmont in stakes-record time. On March 13, 2010, when Rachel Alexandra lost the New Orleans Ladies in her debut as a 4-year-old, the 6-year-old Zenyatta answered at Santa Anita with a victory in the Santa Margarita Handicap.\r\nIn the end, there was only that one fleeting moment when Rachel Alexandra and Zenyatta could have been embraced at the same place and time. They were both there at Churchill Downs, on May 1, 2009, Rachel to run that day in the Kentucky Oaks and Zenyatta entered to make her first start of the year in the Louisville Handicap, earlier on the program. Shirreffs took one look at the way the muddy racetrack was being renovated that morning and decided to scratch. Rachel Alexandra, then trained by Hal Wiggans, won the Oaks by 20 1/4 lengths.\r\nPretty thin gruel for a rivalry, but don&rsquo;t hold that against them. Remember instead the feast they have provided otherwise.