By Mark Trevelyan

RIO DE JANEIRO (Reuters) - Two days after their tense clash in the final of the 100 meter breaststroke, Lilly King of the United States and Russia's Yulia Efimova both came through their morning heats in the 200m, but well behind leader Rikke Moller Pedersen of Denmark.

King, gold medalist in the 100, was fifth in her heat and squeezed through in 15th place out of 16 to Wednesday evening's semi-finals with a time of two minutes 25.89 seconds.

Efimova, the silver medalist on Monday and Olympic bronze medalist in the 200 in 2012, came third in her heat, despite finishing strongly, and qualified in eighth place with 2:23.90.

With two past doping suspensions, the Russian was initially excluded from the Rio Games but succeeded in a last-minute appeal last week to be allowed to compete.

Comments by King describing her rival as a drug cheat have sharpened the rivalry between the two, and Russian swimming chief Vladimir Salnikov told Reuters on Tuesday the atmosphere surrounding his team reminded him of the Cold War.

Efimova, showing the strain of months of uncertainty over whether she would make it to Rio, was distraught after losing to the American on Monday, when she was resoundingly booed by the crowd.

Asked how she was feeling now, the Russian replied with one word: "Great."

King, referring to the storm of controversy over her comments, said: "It's been a little overwhelming to be honest, but you know I'm still just trying to get off my phone a little bit and focus on my race and see what happens after that."

"My parents raised me to say what I wanted to say even if it wasn't what people wanted to hear necessarily, so it's always been like how I am, and I'm going to stick with my guns."

Efimova will swim in the first evening semi-final, and King in the second.

Denmark's Pedersen swam 2 minutes 22.72 seconds, ahead of Japan's Rie Kaneto on 2:22.86 and Australia's Taylor McKeown on 2:23.00, with Britons Chloe Tutton and Molly Renshaw qualifying fourth and fifth.

Asked about the King-Efimova firestorm, Kaneto told reporters: "It's a free country, I don't care what people say. What I think is in my heart."

In other afternoon action, Russia's Evgeny Rylov, Xu Jiayu of China and Australia's Mitch Larkin were the first three in the heats of the men's 200m backstroke, a second chance for Larkin after missing out on a medal in the 100m.

The U.S. 4x200m freestyle relay team of Allison Schmitt, Missy Franklin, Melanie Margalis and Cierra Runge was fastest in qualifying for Wednesday night's final, ahead of Australia and China.

(Reporting by Mark Trevelyan; Editing by Alison Williams)