World and Olympic champion Michael Phelps eased into the semifinals of the men's 100 metres butterfly at the world swimming championships on Friday, though his main rival for the title, Milorad Cavic of Serbia, failed to qualify.
Phelps, who is also the world record holder, was third in his heat in 51.95 seconds and qualified fifth fastest in the Shanghai pool.
Cavic will miss out after clocking 52.67, the 18th fastest time. Only the fastest 16 make the semi-finals.
Cavic was pipped for the Olympic gold medal by Phelps in Beijing when the American, realising he was too far away from the finish to glide into the finish, took an extra stroke and slammed into the wall to beat the Serb by 0.01 seconds.
World and Olympic champion Cesar Cielo of Brazil, Nathan Adrian of the United States and George Bovell of Trinidad and Tobago, were the fastest qualifiers in the men's 50 freestyle, all clocking 22.03 seconds.