Santos landed a flush right to drop Yamanaka right off the bell. Yamanaka got back to her feet, but Santos inundated her with another flurry of shots. The fight was stopped at just 16 seconds in the first round.
[ Related: Gilbert Melendez holds onto belt with decision win ]
"I'm very happy. I trained hard for a year and a half, and I want to fight more. This was a Christmas gift for you guys," Santos said after the bout. Showtime commentator asked her about a bout with up-and-coming fighter Ronda Rousey.
"I think she speaks too much. I'm ready anywhere, any time."
Santos has cut through the women's featherweight division and doesn't have many other opponents of interest. Her last four fights have ended in a TKO or KO, and her record stands at 11-1. Yamanaka, who has spent most of her career in the Japanese promotion Jewels, is now 12-2.
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