by Stephanie CrosbyOpening day at Churchill Downs could determine a Derby contender. The 42-day spring meet starts tomorrow.Spokesperson Darren Rogers says the tenth race is the Grade-three Cliff’s Edge Derby Trial.“The two marquis horses trying to get into this year’s Kentucky Derby are Eightyfiveinafifty, he’s the 8-to-5 favorite, and Pleasant Prince, who is the 4-to-1 second choice," says Rogers. "If either one of them wins, I’d expect them to be in the starting gate on the first Saturday in May.”He says another exciting match-up could come later in the meet, when the unbeaten Zenyatta could compete in the Stephen Foster Handicap on June 12th.“She has been mentioned as an early possibly for that race," says Rogers. "And, of course, stabled right here on our backside, we have Rachel Alexandra, who, if she runs well over Derby week, could be pointed toward that effort and that’s the showdown everybody wants to see.”Rachel Alexandra is last year’s Preakness Stakes winner and Horse of the Year.Rogers says another highlight of the spring meet is four evenings of night racing in June and July.