( CNN ) -- Michael Phelps claimed his third gold of the world swimming championships in Shanghai Saturday but then admitted he was short of peak fitness . The American superstar won the 100m butterfly ahead of Poland 's Konrad Czerniak and compatriot Tyler McGill in 50.71 seconds . It was his sixth medal of the meet in his return to China where he took an unprecedented eight gold medal tally in the 2008 Beijing Olympics . Phelps , who has been overshadowed by teammate Ryan Lochte in Shanghai , said he would be looking to improve with next year 's Olympics in London his target . `` I 'm not in the right shape physically . I want to be faster . It 's a tough race , '' Phelps told AFP . In other action Saturday , controversial Brazilian star Cesar Cielo earned his second sprint title in the men 's 50m freestyle with a winning time of 21.52 seconds . Olympic champion Cesar was only cleared to compete in the championships when a special hearing of the Court of Arbitration in Sport let him off with a warning after he tested positive for a banned diuretic in May . His appearance at the championships has drawn criticism for fellow swimmers and Cielo admitted it had taken its toll . `` For now , it 's a big relief for me . I 've had a crazy month and it 's good to finish with a gold , '' he told AFP . `` I think that shows a lot of mental control . I think I became a more mature person . Even though I 'm 24 , I feel like I 'm 44 right now . It was definitely the biggest challenge of my life . '' Missy Franklin of the United States , who is only 16 , showed she will be a force at the London Games with another two gold medals . Franklin took the women 's 200m backstroke from Australian Belinda Hocking and then helped the U.S win their first 4x100m medley in more than a decade . Britain 's double gold medal winner from the Beijing Games , Rebecca Adlington took her first world title as she edged out Lotte Friis of Denmark in the final length of a thrilling women 's 800m freestyle with America 's Kate Ziegler third . Dutch swimmer Inge Dekker was an upset winner of the women 's 50m butterfly to claim her first individual world title .
Michael Phelps wins his third gold of the world swimming championships . Phelps wins 100 m butterfly but admits he is short of peak fitness . Swimming superstar Phelps has a record 25 world titles . Mexico 's Cesar Cielo wins 50 m free for his second gold in Shanghai .