Phelps, denied trebles in London in the 400m medley and 200m butterfly, delivered a vintage performance to win in 1min 54.27sec and collect his 20th career Olympic medal -- and his 16th gold.

American Ryan Lochte, the world champion and world record-holder, took silver in 1:54.90 and Laszlo Cseh of Hungar earned bronze in 1:56.22.

Although it was his first individual gold of the 2012 Games, there was no fist-pumping celebration from Phelps but instead a smile of quiet satisfaction as his mother and sister cheered from the stands.