Jockey Patrick Valenzuela and trainer Doug O'Neill got off to a winning start on the Breeders' Cup Championship Day card at Churchill Downs when the former claiming horse Maryfield posted a convincing victory in the day's first race, the $238,200 Emirates Airline Very Subtle Stakes.A 5-year-old Elusive Quality mare owned by Empire Stables, Mark Gorman and Jim Perry, Maryfield assumed the lead shortly after the break in the six-furlong test and never relinquished it while pursued by High Heritage. The mare, coming off a fifth-place finish in the Thoroughbred Club of America (gr. III) at Keeneland, set fractions of :21 3/5, :44 3/5, and :56 3/5, with a final time of 1:09 3/5 over a fast track. She ended a six-race losing streak Saturday.The victory was the first stakes success at Churchill Downs for the California-based O'Neill, who was scheduled to saddle Classic contender Lava Man and other contenders Breeders' Cup World Championship races later in the day."It's an incredible way to the start the day," said O'Neill. "She broke a little slow again today, but she had enough room to sneak up there and take it to them." The winner paid $11.40, $6.80, and $4.20. Morner, ridden by Javier Castellano, closed in the stretch to finish second, returning $9.00 and $5.40. Hot Storm, the 4-1 favorite who was among the early stalkers under Garrett Gomez , paid $3.20 for third.Bred in Ontario by Mike Carroll and John C. Harvey Jr., Maryfield has won six of 20 starts. The winner's share of $140,301 pushed her lifetime earnings to $438,001. Claimed for $50,000 at Santa Anita in January, the mare has since won the Flower Girl Handicap and finished second in three stakes, including the A Gleam Handicap (gr. II) at Hollywood Park July 1.True and True finished fourth. Fiery Pursuit, Dixie Dreamer, Prospective Saint, Maggie Slew, Annika Lass and High Heritage completed the order of finish. The field was reduced to 10 with the late scratches of Indian Flare, Joint Effort, Trippi Street and Humorous Gal, all of whom had run two days earlier in the Chilukki Stakes (gr. II) at the Louisville track.