Untapable won the $2 M Breeders' Cup Distaff by 1 1/4 lengths, making Rosie Napravnik the first female rider to win the race in its 31-year history.
Napravnik then stunned the crowd at Santa Anita and a national television audience by announcing she will retire Sunday, revealing that she is seven weeks pregnant.
Untapable, the 3-year-old filly ran 1 1/8 miles in 1:48.68 on Friday at Santa Anita and paid $5.20, $3.40 and $2.60 as the 8-5 favorite in the field of 11.
Don't Tell Sophia returned $4.60 and $3.40, while Iotapa was another nose back in third and paid $4 to show.
Napravnik pumped her right hand after crossing the finish line, having secured her second career Breeders' Cup victory. It was the fifth Cup win for trainer Steve Asmussen, and his biggest since winning the $5 million Classic with Curlin in 2007.
Untapable lugged in on Iotapa on the rail in the stretch, but the stewards did not post the inquiry sign.
It was Untapable's fourth Grade 1 win of the year, including the Kentucky Oaks in May.