World champion Cesar Cielo Wednesday said eye-catching Australian James Magnussen was hot favourite to snatch his 100m title after he eclipsed American great Michael Phelps in the 4x100m relay. The Brazilian, who emerged from a doping storm to clinch 50m butterfly gold, said Magnussen would be unstoppable in Thursday\'s final if he repeats the 47.49sec that helped dethrone triple defending champions the United States. Magnussen, the 20-year-old \"Port Macquarie Missile\", timed 48.21 in Wednesday\'s heats behind William Meynard of France with Italian Filippo Magnini third and Cielo fourth. The semi-finals are later on Wednesday. \"Magnussen is the favourite,\" Cielo said. \"Magnussen should be able to do it (47.49) again. I don\'t know what I can do if he does it again. I don\'t think anybody (can catch him).\" Cielo has endured a turbulent start to his championships after athletes whistled and one gave the thumbs-down to his butterfly win, just days after he was let off with a warning for testing positive for a banned diuretic. Meanwhile Olympic champion Phelps won his 200m individual medley heat but still timed slower than Ryan Lochte, the team-mate who handed him a shattering defeat in the 200m freestyle final. Phelps said Wednesday evening, when he will compete in the 200m butterfly final and the medley semis, would be his toughest in Shanghai as he chases a possible five gold medals, with two already gone begging. \"A big thing is getting through tonight and then it\'s sort of downhill,\" Phelps said. \"My getting ready for the 200 fly tonight, being able to come back and do a double (swim) is going to be fun.\" Phelps\'s loss-strewn year has not improved so far in Shanghai but he insists he is on track to finish his historic Olympic career with a flourish next year in London, when he will try to add to his 14 Games titles. In Wednesday\'s other heats, Australia\'s two-time defending champion Jessicah Schipper was ninth fastest in the 200m butterfly, and Russia\'s Anastasia Zueva was quickest in the 50m backstroke.