Michael Phelps, trying get his sputtering Olympic campaign in gear, cruised into the semi-finals of the 200m butterfly on Monday as team-mate Ryan Lochte prepared for an assault on the 200m free.

Phelps, who rewrote Olympic history four years ago when he became the first athlete to win eight golds in a single Games to take his all-time tally to 14, has yet to strike gold in London.

After barely scraping into the final of the 400m medley, he was shut out of the medals in fourth place.

Phelps delivered an impressive 47.15sec second-leg in the 4x100m freestyle relay on Sunday night, but was denied gold as France seized the victory over America on the final leg.

"I think getting last night out of the way was something that I needed," said the superstar, who added his 400m medley disappointment had nothing to do with confidence but was just a poor swim.

He pronounced himself satisfied with his fifth-fastest time in the 200m butterfly heats, led by Austrian Dinko Jukic ahead of American Tyler Clary and Serbian Velimir Stjepanovic.

"I am pretty happy about this morning, that is all I need to be," said Phelps, who has held the 200m fly world record since 2001 and hasn't been beaten in a major international competition in the event over the same span.

Lochte, who opened the Games with a dominant victory in the 400m medley, is part of a stellar cast in the 200m free final that includes China's 400m free gold medallist Sun Yang, French relay hero Yannick Agnel, South Korean star Park Tae-Hwan and world record-holder Paul Biedermann of Germany.

Three other individual finals on tap Monday night promised explosive action: the men's and women's 100m backstroke and the women's 100m breaststroke.

Australian Emily Seebohm flirted with the world record in the women's 100m back heats, while American Matt Grevers dipped below the 53-second mark in the men's 100m back semis.

Seebohm will be up against Chinese world champion Zhao Jing and world silver medallist Anastasia Zueva of Russia along with world record-holder Gemma Spofforth of Britain and US teenager Missy Franklin in the final.

Grevers heads a strong field that includes France's world champion Camille LaCourt and British hope Liam Tancock.

Ruta Meilutyte, the 15-year-old Lithuanian who set a European record in the 100m breaststroke semi-finals, will try to cap her dream run with gold in a final that includes reigning Olympic champion Leisel Jones, former world record-holder Rebecca Soni and experienced Russian Yuliya Efimova.

Chinese teenager Ye Shiwen launched her bid for a medley double as she led the way into the semi-finals of the women's 200m IM ahead of Beijing silver medallist Kirsty Coventry and American Caitlin Leverenz.

Beijing gold medallist Stephanie Rice also made it safely through, along with US world record-holder Ariana Kukors.

Ye, who used a blistering freestyle leg to seize the women's 400m medley gold in a world record time on Saturday, bristled at suggestions her success was too good to be true.

"There is no problem with doping," the 16-year-old told interrogators in the mixed zone. "The Chinese team has a firm policy so there is no problem with that."

Federica Pellegrini showed she won't give up the 200m freestyle title she won in Beijing without a fight as she led the way into the semi-finals with time of 1:57.16.

France's Camille Muffat, bidding to add to the first Olympic gold she claimed in the 400m free on Sunday night, worked the cobwebs out with a heats swim of 1:58.49, making it safely into the semis with the 12th-fastest time of the morning.

Muffat could still barely believe she had become just the second French woman to win Olympic swimming gold.

"I kept getting up and opening the drawer the medal was in to check it was real and not a dream," she said. "It is so beautiful."

America's 400m silver medallist Allison Schmitt clocked the second-fastest time of the morning and team-mate Missy Franklin was third-quickest as she geared up for her busy night at the pool.

"I didn't expect to go that fast this morning, but it was a great race and it was fun to get out there," said the 17-year-old Franklin. "It's going to be fun tonight, I need to keep my energy up as much as possible."