Olympic champion Claressa Shields led a trio of American boxers who clinched medals at the women's world championships by winning their quarterfinal bouts on Friday.
The 19-year-old Shields took every round against Iaroslava Iakushina of Russia in the middleweight division at Jeju, South Korea.
Reigning world champion Tiara Brown continued her title defense in the featherweight division and Marlen Esparza advanced in the flyweights.
Three other U.S. boxers fell short in the quarterfinals, with Danyelle Wolf, Heidi Henriksen and Krystal Dixon losing on Friday. Wolf, from San Diego, came up short in a close bout against Elena Vystropova of Azerbaijan.
Russia leads all nations with five boxers remaining in the competition. China has four.
The championships will take a day of rest before resuming with semifinal bouts on Sunday.