His majestic display came on a day that Hungary’s ‘Iron Lady’ Katinka Hosszu took her third gold of the week while American gymnast Simone Biles made a flying start to her bid for a record five Rio Olympic golds. But tennis star Serena Williams crashed out of what could be her final Games.
Phelps beat Japan’s Masato Sakai by just four hundredths of a second to take the 200m butterfly and later anchored the US 4x200m freestyle relay team to victory.
At 31 — the oldest individual Olympic swimming gold medalist ever — Phelps is still the master of the pool.
After claiming his 20th title in five Olympics — beating old rival Chad le Clos in the process — Phelps stood in the water striking a pose like a Roman emperor, soaking up the acclaim.
The 200m butterfly was his first world record in 2001 and he was determined to win back the Olympic title he lost to South Africa’s Chad Le Clos in 2012. But Phelps said that was also the last time he would race it.
“That event is kind of like my bread and butter,” Phelps said.
“There wasn’t a shot in hell I was losing that race,” he added. “And if I did, I was leaving everything in the pool.”
Phelps returns on Wednesday for the heats and semi-finals of the 200m individual medley.
But nothing could beat Tuesday night’s dramatic action in the pool, with Hosszu completing the individual medley double by winning the 200m final in an Olympic best 2:06.58.
Katie Ledecky, leading the new generation of American swimming stars, captured her second gold of the Games by holding off a brave charge from Sweden’s Sarah Sjostrom to take the women’s 200m freestyle final in 1:53.73.
The United States is also looking forward to a new era of gymnastics domination with Biles helping the USA women’s team to victory by eight points over Russia.
She is aiming for an unprecedented five titles this week.
“It’s everything and more than I’d hoped it to be,” said the tiny 19-year-old Texan who has set gymnastics alight with 10 world titles in the past three years.
As her Olympic odyssey got underway, another crumbled as defending tennis champion Williams suffered a shock 6-4, 6-3 defeat to Ukraine’s Elina Svitolina in the third round.
Williams, hampered by a shoulder injury, served five double faults in one game of the second set as her own bid to reach five gold medals ended.
The 34-year-old and her sister Venus were knocked out of the women’s doubles, the three-time champions’ first ever defeat together in Olympic competition.
“It was a great opportunity. It didn’t work out the way I wanted it to, but at least I was able to make it to Rio. That was one of my goals,” she said.
French Open champion Garbine Muguruza also crashed out, losing 6-1, 6-1 to Monica Puig of Puerto Rico.
In diving, competitors were perplexed to find the water had turned from light blue to green overnight, although organizers insisted it was safe.
China’s Chen Ruolin shrugged off the colour-change to claim a record-equaling fifth gold medal in the women’s synchronized 10m platform, with partner Liu Huixia.
New Zealand’s rugby hopes took a blow when superstar Sonny Bill Williams suffered a tournament-ending injury in their shock 14-12 opening defeat to Japan.
France won their first gold of Rio in the equestrian team events. French hero Astier Nicolas also took a silver in the individual event behind Germany’s Michael Jung.
Chinese weightlifter Deng Wei won the women’s 63kg category with a world record after Taiwanese rival Lin Tzu-chi pulled out amid reports of a failed dope test.
Fears over Olympic security meanwhile flared anew, after a bus carrying accredited press was attacked in Rio late Tuesday.
It remained unclear whether gunfire or stones were used in the media bus attack, which smashed windows and slightly injured two journalists, according to Rio organizers.