Shanghai - America's Ryan Lochte stunned 14-time Olympic champion Michael Phelps to win the 200m freestyle world title on Tuesday and extend his team-mate's rocky start to the meeting in Shanghai.
Lochte surged from third place over the final 100 metres to finish in 1:44.44, 0.35 seconds ahead of Phelps with Germany's Paul Biedermann, the defending champion and world record-holder, third.
Phelps, who won this event and seven others at the Beijing Olympics, can now win a maximum five gold medals, the same number he claimed in Rome two years ago.
Phelps has said he is into the final year of his career as he builds towards London 2012, where he will aim to add to his 14 Olympic titles - including the record-breaking eight in Beijing.
The 26-year-old Baltimore Bullet admits he has struggled for motivation in recent years, and has slumped to a series of shock defeats this season. But he says he is back on track and training well under coach Bob Bowman.
Phelps arrived in Shanghai with 22 world titles but suffered a disappointing start to the championships when the United States finished third in the 4x100m freestyle, ending an unbeaten world and Olympic streak stretching back to Athens 2004.
In 2009, Biedermann beat Phelps by a wide margin at Rome's Foro Italico and shattered his world record with a time of 1:42.00, the American's first major international defeat in four years.