LOUISVILLE - Imagine settling into a U2 concert, ready to be blown away by Bono, and who shows up to warm up the crowd?\nElvis.\nThat is exactly the feel this week at Churchill Downs, where an eager-to-please field of callow Derby colts is about to be upstaged by the queen herself, Zenyatta. They are roadies to her rock star. Satellites to the sun. And if you doubt it, witness the scene Wednesday morning at a quarter past nine, when the big mare emerged from Barn 45, scattering a healthy crowd gathered to hear Larry Jones hold forth about Friesan Fire.\n"It's her," whispered an onlooker.\n"She's here?" another exclaimed.\n"My God, how big is she? Sixteen hands?" wondered yet another, and from high atop Zenyatta, Steve Willard was heard to reply, with full pause for effect:\n"Seventeen . . . one."\nZenyatta is at Churchill Downs to begin her 5-year-old season in the Louisville Distaff on Friday. She has gone nine races without losing, and if there is a serious roadblock in the Louisville field, her identity is not readily apparent. Zenyatta has not traveled this far from her California comfort zone since winning the Apple Blossom Handicap at Oaklawn 13 months ago, but if the trip bothered her, you could not tell by watching the look of abject admiration on the face of trainer John Shirreffs as Big Mama pranced and snorted on her way to the track.\nShirreffs was asked if the champion had changed at all from 4 to 5.\n"Mares don't usually," he replied. "If anything, though, I think she's stronger."\nThe idea of a stronger Zenyatta is a little scary. Pity the poor things who get in her way. Still, each season brings forth new talent, untroubled by comparisons to established stars. At one time or another, Zenyatta has dealt with Ginger Punch, Cocoa Beach, Music Note, Hystericalady, and Tough Tiz's Sis, but that does not mean there's not something in the weeds, ready to test her anew.\nIn fact, we might find out about that later Friday afternoon when Rachel Alexandra plays the part of Zenyatta in the 135th running of the Kentucky Oaks. As the two most famous female Thoroughbreds in America, their joint appearance should make for a day not even the rain can ruin. It might even be a long-lens preview of a possible showdown this fall in the Breeders' Cup Ladies' Classic.\nZenyatta was doing nothing but burning day money when her chance at running in the 2007 version of the Kentucky Oaks came and went. Still evolving, she did not make her first start until November of that year. Things have gone well since.\nRachel Alexandra, on the other hand, is already a grizzled veteran of nine starts, with six wins over four different tracks, including her last four in a row. She races for her breeder, Dolphus Morrison, and his partner Mike Lauffer. Hal Wiggins is her trainer.\nIt was Hal Wiggins standing outside his Churchill Downs barn Wednesday morning, wearing a Texas A&M cap and pleased as could be that anyone would think enough of him or his filly to drop by.\n"I've been here long enough to know that on Sunday morning after the Derby, this place is a ghost town except for the crowd around one barn," Wiggins said. "And that's okay. I've never had very much to write about."\nUntil now. Rachel Alexandra, named for Morrison's granddaughter, was a few yards away, killing time, batting a tetherball around the mouth of her stall as her groom, Ruben Flores, worked nearby. After her lickity-split workout last Monday (the sound barrier was threatened), Wiggins gave her an extra day of walking on Wednesday, more to calm the trainer than restore the filly.\n"You know, she has never had a sick day in her life, even as a 2-year-old," Wiggins said. "I probably shouldn't say that before this race. But you see that in really good horses. And her disposition . . . she's just a pleasure. She did work a little too fast the other day, but she did that in front of the Fantasy, too. Not quite that fast, but too fast."\nFor the record, Rachel Alexandra won the Fantasy by 8 3/4 lengths.\nWiggins is 66, and while Rachel Alexandra is the best he's ever trained, he can draw on his earliest racetrack experiences for context. He was 14 when he worked for W.A. "Ab" Simpson, who trained the champion Quarter Horse filly Stella Moore. By the time Wiggins came along, Stella Moore's sons and daughters were making noise all over the Southwest.\n"She was a black mare with a bald face," Wiggins recalled. "They once matched Stella Moore and the Thoroughbred Olympia going a quarter-mile at Tropical Park. I'm not making excuses, but a quarter-mile was way too far for her. He beat her, but he knew he'd been in a race."\nThat was Jan. 5, 1949. Four months later Olympia went postward the odds-on favorite in the 75th Kentucky Derby. He finished sixth.\nWiggins never gave running Rachel Alexandra in the Derby a second thought. He is, however, looking forward to the day when his filly might take on Zenyatta. If that happens, he'll know she has done well enough to earn the chance.\n"I was there and watched Zenyatta race at Oaklawn last year, and paid close attention to her since," Wiggins said. "I've got a lot of admiration for her. I really do. I just hope we're both sound and we meet in November."