Shields, the first American woman to win a boxing gold medal with middleweight honours at London 2012, then followed that up with victories at the 2014 World Championships and 2015 Pan American Games.

She continued her superb form with a 3-0 victory over Panama's Atheyna Byion to reach the semi-finals.

Also through to the last four is Canadian second seed Ariane Fortin-Brochu, winner of all three rounds on points against Francelis Dilmar Carmona-Paez of Venezuela.

Brazil's Andreia de Oliveira Bandeira overcame Argentinian rival Lucia Noelia Perez 2-1 and Dominican Republic's two-time Pan American Games silver medallist Yenebier Adelina Guillen Benitez beat Alma Nora Ibarra Vasquez of Mexico, 3-0.

Shields' compatriot Virginia Fuchs was among other US winners today, beating Suelm Urbina of Mexico in the under 51kg division.

Mikaela Mayer made it three from three with victory over Canada's Caroline Veyre in the under 60kg event.

There was defeat for Antonio Vargas as preliminary action continued in the men's event.

He was beaten 3-0 on points by Dominican Republic's Leonel do los Santos Nunez in the under 52kg category. 

Action also reached the quarter-final stage at the African Qualification event in Yaoundé, with Algerian top-seed Zoheir Toudjine among those progressing.

He beat Cameroon's Fotsala Simplice 3-0 in the under 49kg light flyweight division.

Other winners included Namibian second seed Mathias Tulyoongelini Hamunyela. who beat Morocco's Imad Ahyoun, 2-0 on points.