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RIO DE JANEIRO — In a showdown that came out of nowhere and took on Cold War overtones, outspoken American Lilly King took down controversial Russian rival Yulia Efimova in the 100-meter breaststroke Monday night.

King earned international attention – and no small degree of admiration – for both gesturing and voicing her disapproval of Efimova’s doping past during the semifinal heats Sunday night.

Then the fiery 19-year-old Olympic rookie from Evansville, Indiana, backed it up with medals on the line Monday. King held off the late-charging Efimova to win a thrilling race by just over half a second, finishing with an Olympic-record time of 1:04:93.

It was America’s first female gold medal in the 100 breast since 2000.

Efimova had to settle on silver with a time of 1:05:50 while King’s teammate, Katie Meili, will take home a bronze medal with a time of 1:05:69.

Efimova, the 2015 World Championship gold medalist in this event, has twice tested positive for banned substances and was initially among the athletes prohibited from competing in the Rio Games by the International Olympic Committee. However, a legal challenge granted her late entry into the competition, to the dismay of many of her competitors. Efimova was booed by the crowds at the Olympic Aquatics Stadium both Sunday and Monday.

King, who will be a sophomore at Indiana University this fall, will swing back into action later this week. She will compete in the 200 breaststroke, where she is a long shot to win a medal, and will be on the American 400 medley relay Saturday.