In what's believed to be a record margin of victory, 1-5 favorite Rachel Alexandra finished 20-and-a-half lengths ahead of the rest of the field to capture the 135th Kentucky Oaks at Churchill Downs Friday.With Calvin Borel aboard, Rachel Alexandra broke away from pacesetter Gabby's Golden Gal at the final turn to win the $554,500 stakes race for fillies only.Rachel Alexandra is owned by L & M Partners, LLC and trained by Hal Wiggins.The second-place finisher was Stone Legacy; Flying Spur came in third.Churchill Downs says Oaks Day attendance was 104,867,