Michael Phelps began the final chapter of his storied career with a golden hue on Sunday as he helped the U.S. men's team to victory in the 4x100 metres freestyle relay to collect his 23rd Olympic medal.

With the U.S. men having medalled in every Olympics 4x100 freestyle relay since the event was introduced in 1964, there was every chance Phelps was going to add to his haul.

Swimming second in the relay, Phelps took over from Dressel, just 0.02 seconds behind France and in a few powerful strokes the 31-year-old gave his team the lead.

"Caeleb wanted to get out in open water, lead us off and the only thing I said to them 'I'm going to try and get you guys as much open water as I can'," said Phelps.

"I know how hard it is to swim in the wake in that race and I was going to do whatever I could to get them out front."

Held increased the lead and London individual 100 freestyle champion Nathan Adrian brought them home as the chants of "USA!" "USA!" rose to a crescendo.

"It was crazy, I was standing on the block while Caeleb (Dressel) was coming in and I actually thought my heart was going to explode out of my chest," said Phelps.

 " Having the amount of excitement cheering in the stands during that race I don't know if I have heard anything like it."

It was not unusual to see Phelps, who returned for one last tilt at the Olympics after initially retiring following the London Games, standing on the podium, but it was to see the 19-time champion overcome with emotion.

The victory was too much for Held and Dressel, who won their first Olympic medals and had to be consoled by their vastly-experienced team mate.

With his team mates in tears, Phelps smiled and laughed and hugged them as they took a victory lap around the pool deck, until he saw his fiancée and baby son in the stands.

"The younger guys started crying and I started crying," laughed Phelps.

"They were making us cry.