Phelps safely through to 100 butterfly semi-finals

ROME (Reuters) - Olympic champion Michael Phelps won his heat to qualify easily for the 100 butterfly semis as he began the defense of his world title on Friday.

The American, who retained his 200 butterfly crown on Wednesday with a world record, clocked 50.9 seconds, the joint-second quickest.

Serbia's Milorad Cavic, who won the 50 butterfly title on Monday, was fastest with a time of 50.56 while Phelps' time was equaled by compatriot Tyler McGill.

"I did what I wanted to do," Phelps told reporters. "I think it's going to be between me, Cavic, (Spain's Rafael) Munoz and (Australia's Andrew) Lauterstein in the final. There's a bunch of real good butterfliers there."

Brazil's Olympic champion Cesar Cielo Filho, who broke the 47-second barrier to win the 100 freestyle with a world record on Thursday, set a new championship mark of 21.37 to reach the 50 freestyle semis.

Swede Stefan Nystrand was next on the timesheet after he beat French world record holder Frederick Bousquet into second place in their heat.

Defending champion Therese Alshammar was quickest in the women's 50 butterfly, going through to the next round in 25.44 to beat a championship record set in a previous heat by her Swedish compatriot and fellow qualifier Sarah Sjostrom.

Dutch world record holder Magdalena Veldhuis made it to the semi-finals with the second top showing.

But Australia's Libby Trickett, whose titles include the 100 butterfly Olympic crown, missed out after clocking the 17th best time.

"It was so fast here. I'm pretty sure my time would have made a final in 2007. I knew this would be the toughest event to get through," said Trickett, who will defend her 100 freestyle title in the final later on Friday.

"I'm a bit upset, but what can you do? Just keep going and move on."

Zimbabwe's Olympic champion Kirsty Coventry eased into the women's 200 backstroke semis by setting a new championship record of 2:06.72.

Britain's new 100 backstroke world champion Gemma Spofforth looks to be the world record holder's biggest threat after she set the next best time of 2:07.69.

But China's Zhao Jing, who took gold in the women's 50 meters backstroke on Thursday with a world record time, was well off the pace and failed to qualify.

Olympic and defending world champions the United States, without Michael Phelps in the team, finished joint top to reach the 4x200 men's freestyle relay final after an exciting dead heat with Japan.

Olympic champion Rebecca Adlington qualified first for Saturday's women's 800 freestyle final, just ahead of fellow Briton Joanne Jackson, who also won her heat.

Chile's Kristel Kobrich Schimpl and France's Ophelie-Cyrielle Etienne will both take part in a nine-swimmer final after they finished joint eighth on the same time.

Officials had originally said the pair would have a 'swim-off' later on Friday.