By Mark Trevelyan and Jack Stubbs
RIO DE JANEIRO (Reuters) - Lilly King of the United States won the Olympic gold medal in the women's 100 meters breaststroke on Monday, denying Russia's Yulia Efimova who was greeted with resounding boos from the Rio de Janeiro crowd.
Katie Meili of the United States took the bronze, with London 2012 champion Ruta Meilutyte of Lithuania fading in the second length to finish seventh.
There were loud jeers before the start of the race for Efimova, who has twice been suspended for doping offences.
The 24-year-old world champion won a legal challenge last week to get herself reinstated to the Olympics, having previously been excluded because of her doping record.
King swam a strong first 50 meters and led at the turn, with Efimova well back in fourth place. The Russian surged forward in the second half of the race and appeared to be catching her rival, but King finished powerfully in an Olympic record time of one minute 4.93 seconds, with Efimova 0.57 seconds behind.
"It just proves that you can compete clean and still come out on top," King said. Before leaving the poolside, she patted the Russian on the back.
Efimova, who after months of uncertainty learned only last Friday that she could compete, broke down after the race in front of reporters, crying into the arms of a friend.
"I can't say that I'm happy, it's just good that I was able to compete," she said.
"I can't remember the last time I slept properly ... I've been completely without sleep for the last month. The last three weeks in particular were horrendous."
The Russian said had wanted to win gold to prove her critics wrong.
"That's why I'm so upset that I didn't manage it, I knew that lots of people were counting on me."
After the victory ceremony, the two Americans wrapped themselves together in the Stars and Stripes flag, while Efimova stood awkwardly to the side.
The margin was more comfortable than in the heats and semi-finals, where King had beaten her rival by 0.01 and 0.02 seconds respectively. Efimova was also jeered at both those swims.
Revelations of state-sponsored Russian doping overshadowed the build-up to the Olympics and led to more than 100 competitors being excluded, including the country's entire athletics and weightlifting teams.
Russia was banned on Sunday from the Paralympics that will follow.
Efimova was one of several Russians who successfully argued in legal appeals last week that having served their original doping suspensions, they should not be punished again for the same offense by being barred from Rio.
She was banned between October 2013 and February 2015 after testing positive for traces of the anabolic steroid DHEA, and also briefly suspended after testing positive for meldonium this year.
(Editing by Greg Stutchbury)