Images from the Olympics swimming action at the La Defense Arena, Paris, on Thursday.
The 22-year-old, nicknamed the "French Michael Phelps", carried the expectations of a nation into his first event but he simply crushed his rivals in a swim of four minutes and 2.95 seconds that broke the Olympic record and flirted with his own World record mark.
Phelps has 28 total Olympic medals, showed on Thursday he could also throw a useful baseball pitch.
For almost 20 years, Michael Phelps was swim coach Bob Bowman's project. But Phelps, who retired from swimming as the most decorated Olympian of all time after winning a record 22 medals including 18 golds, is now swing guru Hank Haney's project as he turns his sights on becoming a top golfer.
Michael Phelps has dropped the 200 metres freestyle from his schedule for next month's London Olympics, leaving him with seven events for his Games swansong.
Michael Phelps will contest at this week's Pan Pacific Championships in California and is expected to win a host of medals at the event.
American Michael Phelps should stay out of international competition until swimming's governing body FINA sorts out the chaos over swimsuits, his coach Bob Bowman said on Tuesday. FINA has agreed to ban performance-enhancing polyurethane suits next year after a glut of world records but said the new rules may not come into effect until April or May.
The US swimmer will enter five individual events and three relays at the Athens Olympics in his quest to equal or surpass Mark Spitz's record haul of seven gold medals the 1972 Games in Munich.
Phelps said many children are like him, who are afraid of water, and that a non-profit initiative started by him a decade ago has so far taught 30,000 children about swimming.
Having ended his career once in London on what he considered a sour note, Michael Phelps enters the Rio de Janeiro Olympics pool for his second swansong determined to bow out on his own terms.