By Mark Trevelyan

RIO DE JANEIRO (Reuters) - Russia's Yulia Efimova, who won her appeal against a doping ban on the eve of the Rio Olympics, was jeered before and after her 100 meters breaststroke semi-final on Sunday but qualified in second place for Monday's final.

Efimova, the world champion at the distance, clocked one minute 5.72 seconds in the semi-finals, two-hundredths of a second behind American Lilly King.

Both improved on their times in the morning heats, when King had shaded the Russian by 0.01 seconds.

In the first semi-final, Efimova was greeted with boos and klaxons before the start.

Defending Olympic champion Ruta Meilutyte of Lithuania reacted first from the starting block and led at half-way, with Efimova turning in fifth place.

But the Russian moved up the field in the final 50 meters to win convincingly, and wagged one finger in the air as the crowd greeted her with more boos.

King won the second semi-final ahead of China's Shi Jinglin, who qualified third-fastest for the final, with Meilutyte in fourth.

Revelations of state-sponsored Russian doping overshadowed the build-up to the Olympics, and the country was banned on Sunday from the Paralympics that will follow.

Efimova was one of a number of Russians who successfully appealed, arguing that after serving previous doping bans they should not be punished again by being excluded from Rio.

The 24-year-old world champion only learned on Friday that she could compete, ending months of uncertainty.

"I was crazy, like, last half-year, I just don't understand what's going on and everything. I'm just happy to be here and I'm ready to race," she said.

Asked after the morning heats if it was fair she was competing, King said: "You know, I'm going to stay out of it, but a level playing field would be preferred."

Meilutyte declined to comment on her rival's reinstatement.

Efimova is also due to compete in the 200 breaststroke, in which she was world champion in 2013 and won a bronze medal at the London Olympics in 2012.

Efimova was banned between October 2013 and February 2015 after testing positive for traces of the anabolic steroid DHEA. She was also briefly suspended after testing positive for meldonium this year, but cleared in July.

(Reporting by Mark Trevelyan; Editing by Ken Ferris and Alison Williams)