Royal Delta won the Breeders' Cup Ladies' Classic for the second successive season under a front-running Mike Smith ride.
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The winning rider was becoming the most successful jockey in Breeders' Cup history and he was at his strongest down the home stretch as My Miss Aurelia tried to close his partner down.
However Royal Delta, who made all for the first time in her career, fought tenaciously to stake her horse of the year claims.
Include Me Out looked a big threat at the top of the straight but had to settle for third.
Smith said: "She broke extremely well and I just didn't want to get in her way. She was brilliant today.
"Bill has done a great job getting her here 110% for this race. She was great from the time I got on her and I had half a length on the field leaving the gates.
"I thought when you're on a talented horse they are fast for a reason. I was either going to be a big-time hero or end up really bad. I felt confident and she was a true champion today."
Winning trainer Bill Mott added: "Our plan was just not to get in her way. We know she's a staying filly and gets a mile and a quarter.
"We knew there was some speed in there, but we were going to let her go up in the race if she wanted to. With Mike she broke very well today. She let her do her thing and she did the rest.
"She was going easily. I looked at her down the back and she was cruising. I knew that if they ran to her she find out a little more."