Phelps 13.33 seconds with a time that was well off his world record of 4 - 03.84 set four years ago in Beijing .
Phelps is the two - time defending Olympic champion won his heat in 4 minutes .
Phelps , the two - time defending Olympic champion won his heat in 4 minutes , 13.33 seconds with a time that was well off his world record of 4 - 03.84 set four years ago in Beijing .