The Illinois-bred daughter of Summer Squall, trained by Chicago-based Anthony Mitchell, forced the pace while three-wide and closed with determination to edge her rivals in a four-horse photo finish.
"I'm so happy to win a race for this guy (trainer Mitchell)," Douglas said. "He doesn't have many horses but he does such a good job. He gave this filly a rest and she came back stronger than ever. She rates so nicely. I really love her."
Summer Mis posted a final clocking of 1:09.77 on the fast main track, edging Don't Countess Out by a head, with Born to Dance a nose back in third. They were followed, in order, by favored Bauhauser (ARG), Savorthetime, Bruanna, Jodys Deelite, Distinctive Code, Vicki Vallencourt and Crow Jane.
The winner paid $25.80, $10.80 and $6.40. Don't Countess Out returned $7.80 and $4.20. Born to Dance paid $4.80 to show.
With her victory, Summer Mis improved her record to 15-8-1-1 and increased her lifetime earnings to $358,903 in front of 13,246 fans at Keeneland.