RIO DE JANEIRO-American Lilly King vanquished drugs-tainted Russian Yulia Efimova to win 100m breaststroke gold on Sunday in a race emblematic of the doping cloud shadowing the Rio Olympics.

King, a 19-year-old first-time Olypian, had made it clear she didn't think Efimova belonged in the pool, and plenty agreed as the 24-year-old world champion was showered with boos as she took the blocks. King led at the turn and repelled a late Efimova charge to win in an Olympic record of 1min 04.93sec, with the Russian second in 1:05.50. American Katie Miele was third in 1:05.69.

"I think it just proved that you can compete clean and still come out on top," King said, adding that she had no regrets about her comments about Efimova. I'm actually glad I made a statement, and I ended up coming out on top in the race," she said.

While King and Miele celebrated joyously together in the water, Efimova -- who is also entered in the 200m breaststroke in Rio -- hung on her lane rope before departing the pool deck. It was a contrast to the celebrations of China's Sun Yang, another swimmer targeted by his peers for past drugs transgressions who shook off controversy to win the 200m freestyle gold.

Sun took the blocks to cheers from Chinese teammates and supporters in the stands, one group of them seated behind a section of Aussies whose 400m free gold medallist Mack Horton this week branded Sun a drugs cheat -- a reference to his three-month suspension in 2014 for a positive test for a banned stimulant. Third at the 150-meter mark, Sun stormed past early leader Chad le Clos of South Africa to win in 1:44.65.

Le Clos settled for silver in 1:45.20 with American Conor Dwyer third in 1:45.23. "I tried not to get distracted by outside noise," Sun said. "I just tried to be myself. I was more relaxed than for the 400m and that helped me win gold."

Efimova's drugs history is murkier than Sun's. She served a 16-month ban for DHEA before returning to win the 100m world title last year. Since testing positive for meldonium this year she has been banned and reinstated twice in a convoluted case that saw her allowed into the Rio Games at the last minute along with six other Russian swimmers who had either tested positive in the past or been named in the damning report on state-sponsored doping in Russia.

Hungary's Katinka Hosszu claimed her second gold in as many events with a storming victory in the 100m backstroke. The "Iron Lady" was sixth at the turn with world champion Emily Seebohm leading but stormed home to win in 58.45sec. American Kathleen Baker was second in 58.75, just one one-hundredth of a second in front of China's Fu Yuanhui and Canadian Kylie Masse, who shared bronze in 58.76.

Seebohm, meanwhile, not only was unable to improve on the silver medal she earned in London but faded to seventh in 59.19. Little more than an hour later Hosszu was back in action in the 200m individual medley semi-finals, where she's seeking to complete the medley double after winning the 400m IM in a world record on Saturday.

Ryan Murphy extended America's run of dominance in the men's 100m backstroke, coming from fourth at the turn to win in an Olympic record of 51.97sec. It's the sixth straight Olympic gold in the event for the USA. China's XuJiyau was second in 52.31 and American David Plummer captured bronze in 52.40.

Le Clos also pulled double duty, following up his freestyle silver by booking his place in the 200m butterfly final, where he'll defend the title he won in London ahead of superstar Michael Phelps. Phelps made a storming start to his semi-final, leading at every turn only to be overtaken by Hungarian Tamas Kenderesi in the final 30 meters. Kenderesi topped the qualifying times in 1:53.96 while Phelps was second-fastest in 1:54.12 followed by Hungarian Laszlo Cseh and le Clos.