LONDON -- The first U.S. boxer to win a medal at the London Olympics will be a woman.

American flyweight Marlen Esparza and middleweight Claressa Shields each advanced into the semifinal round on Monday to clinch medals.

Esparza, 23, defeated Venezuela's Karlha Magliocco 24-16 and to secure Team USA's first boxing medal of the Olympics.

Shields, 17, beat Sweden's Anna Laurel 18-14 to move forward in the first Olympic women's boxing competition.

The U.S. men were shut out of the medals in London.

Esparza advances to Wednesday's semifinals in a rematch with top-seeded China's Ren Cancan, who captured a 16-8 decision over the native of Houston, Tex., in the semifinals of the Women's World Championships earlier this year.

The winner of Cancan-Esparza will move on to the gold medal final, while the loser will be automatically awarded bronze, as there is no third-place bout in Olympic boxing.

Shields, from Flint, Mich., will fight Kazakhstan's Marina Volnova in the semifinals.