On a fantastic night of action in the pool the most dramatic race was saved until last as the most decorated Olympian in history made his eagerly awaited debut at his fifth Games.
Phelps recorded a storming 47.12 second leg to inspire the USA relay side that included Caeleb Dressel, Ryan Held and Nathan Adrian. Recognising that a 23rd Olympic medal was in his grasp, he banged on his lane blocks as the USA held off France in a time of 3:09.92.
Phelps said the USA wanted to make up for the disappointment of finishing second in the same race at London 2012.
“We wanted that race back so badly. I played that race (the London 2012 race) for the guys in the room the other day. In 2008 we had a great one, in 2012 we fell off a little bit. My last 4x100 relay, it feels damn good to get a win. It was the fastest 100m free of my career.
“Ryan (Held) swam a great race this morning and came back and swum another one tonight. You know Caeleb (Dressel) wanted to get out in the open water and lead us off. The only thing I said to them was, ‘I am going to try and get you guys as much open water as I can’. I know how hard it is to swim in the wake in that race.
“These guys are awesome, they will be there in four years - you got this, I am out.”
On an emotional night Phelps said the atmosphere at the venue was special.
“It was crazy. I was standing on the blocks while Caeleb (Dressel) was coming in and I honestly thought my heart was going to explode out of my chest. Having the amount of excitement and cheering in the stands during that race, I don't know if I have heard anything like it.”
Sweden’s Sarah Sjostrom had set the ball rolling with a new 100m women's butterfly mark, smashing her own record in 55.48 seconds to finish ahead of impressive 16-year-old Penny Oleksiak of Canada.
“The feeling is totally crazy. I didn't realise it was a world record. I knew I was the big favourite,” said Sjostrom. “I was under pressure, so I tried to focus on no disasters. Before the start I said to myself, it's just a pool. It's nothing. I know what to do. I was not so nervous; I was in a good mood today. I knew the hundred metres butterfly was my big chance.”
Adam Peaty produced a dominant performance in the men's 100m breaststroke, breaking the world record for the second time at Rio 2016 to win Great Britain's first Olympic men’s swimming gold for 28 years in a time of 57.13.
Katie Ledecky of the USA, who is unbeaten in international individual competition, won the 400m freestyle in 3:56.46, nearly two seconds faster than her own two-year-old world record.
“3:56 was the goal I set after Barcelona 2013 (world championship) so it feels really good,” said Ledecky. “I’m pumped. I was so close to breaking it this morning. I felt good throughout. The swim was almost identical to this morning, but with a bit more pop on the last lap. It’s pure happiness.”