LOUISVILLE, Ky. - Only races the magnitude of the Kentucky Derby and Kentucky Oaks could prevent the undefeated champion Zenyatta from being the center of attention when she makes her much-anticipated 2009 debut in the $350,000 Louisville, the highlight of the undercard on Friday's Oaks Day program at Churchill Downs.\nThe Grade 2 Louisville is one of five supporting stakes on a 12-race card which begins at 10:30 a.m. Eastern.\nZenyatta will be making her first start since clinching an Eclipse Award with her 1 1/2-length victory over Cocoa Beach in the Breeders' Cup Ladies' Classic more than six months ago. The Ladies' Classic completed a perfect campaign for Zenyatta, a daughter of Street Cry who is undefeated in nine career starts and unquestionably one of the game's brightest stars.\nZenyatta will not be the only unbeaten member of the eight-horse Louisville field. One Caroline has captured all five of her starts, including the Grade 3 Sabin and Grade 2 Rampart earlier this season at Gulfstream Park. Grade 1 winner Unbridled Belle adds further appeal to the 1 1/16-mile Louisville lineup, which is completed by Swift Temper, Miss Isella, Unforgotten, Modification, and French Kiss.\nThe $150,000 Alysheba also figures to draw plenty of attention, bringing together graded stakes winners Macho Again and Ready Set, along with 2008 Travers runner-up Mambo in Seattle.\nMacho Again returns to Churchill Downs for the first time since his victory one year ago in the Derby Trial. He is coming off the most important win of his career, a come-from-behind one-length triumph over a sloppy track in the Grade 2 New Orleans Handicap on March 14. The prospects of similar conditions exist for the 1 1/16-mile Alysheba, with rain predicted for the Louisville area on Friday.\nReady Set has not started since finishing third in Aqueduct's Grade 3 Discovery Handicap on Nov. 22. His most important victory came last summer in the Grade 3 West Virginia Derby at Mountaineer.\nMambo in Seattle's most notable performance came in defeat, a heart-breaking nose setback at the hands of Colonel John in the Travers. Mambo in Seattle has failed to win in four subsequent starts, including a high-level optional claiming race in his 2009 debut at Keeneland on April 5.\nThe potential for rain could have a major impact on the three other stakes on Friday's card - the Grade 3 American Turf, Grade 3 Aegon Turf Sprint, and the Edgewood, all of which are scheduled to be run on the grass.\nCannonball, Chamberlain Bridge, and Due Date, who finished two-three-four in Keeneland's Grade 3 Shakertown, will top the field for the five-furlong Aegon Turf. Cannonball turned in the best race of his career in the Shakertown when beaten a head by Heros Reward after being hung very wide throughout in a race decided over a less-than-firm course.\nGrade 1 winner Laragh figures to be heavily favored to win the 1 1/16-mile Edgewood for 3-year-old fillies. Laragh, winner of the Grade 2 Hollywood Starlet in her 2-year-old finale, returns to the grass after finishing fifth and last making her 3-year-old debut over a sloppy track in the Grade 2 Comely at Aqueduct.\nThe 1 1/16-mile American Turf brings together a field that includes six stakes winners, topped by Stormalory, who exits a neck triumph in Keeneland's Grade 3 Transylvania run over a yielding course. He should face his stiffest competition from the red-hot California invader Battle of Hastings, a stakes winner in each of his last two starts. Bittel Road, Turfiste, and Skipadate are also serious contenders.