AFP - Michael Phelps suffered a rare defeat on Thursday in the 100m butterfly final at the Minneapolis swim meet as he continues his preparations for the 2016 Olympics.

The most decorated medallist in Olympic history was beaten into third place behind winner Giles Smith and San Condorelli in second.

Phelps clocked 52.99 sec, far slower than the 50.45 which he produced at last year's US Swimming Championships, the fastest time over the distance in 2015.

Phelps, winner of a record 18 Olympic gold medals, told Sports Illustrated this week he has rediscovered his zest for swimming after initially retiring following the 2012 London Games.

After an arrest for drink-driving in Baltimore in 2014 he checked himself into rehab and decided to return to Olympic competition.

He has not drunk alcohol since his arrest, and has vowed not to drink until after the Olympics in Rio de Janeiro next August.

Phelps told Sports Illustrated: "You're going to see a different me than you saw in any of the other Olympics."

In other races in Minneapolis on Thursday, US prodigy Katie Ledecky dominated her compatriot Missy Franklin to win the 200m freestyle.

Ledecky came home in 1min 55.37sec, more than a second ahead of Franklin, who clocked 1:56.73. Allison Smith was third with 1:57.28.