Michael Phelps says he was never going to lose the 200 metre butterfly final in a revenge matchup with Chad le Clos in Rio.
Le Clos beat Phelps by 0.05 seconds in the event at the London 2012 Olympics and had created tension with the American due to his ready-room antics during these Games.
But the South African was silenced as his rival led for the last 150 metres to secure the gold medal on Tuesday.
Phelps, 31, insisted defeat in the final was never an option but praised Le Clos after the race, having kept tabs on him throughout.
"I didn't say anything to anybody else, but there wasn't a shot in hell I was losing that tonight," Phelps told reporters after the race.
"I came into the pool on a mission and the mission was accomplished, but the last 10 meters were not fun. Oh my gosh! I thought I was standing still.
"We are competitors. I don't want him to win and I'm sure he does not want me to win. He is a very good racer and is not afraid of putting it on the line.
"The kid has got talent. I knew exactly where he was most of the race.
"He and I have not spoken that much here. That was the first time after the race. Kind of what happened four years ago stuck with me. It was a frustrating race for me and it's good for the sport to be able to have a competitor like that."
Phelps, who later won his 21st Olympic gold in the 4x200m freestyle relay alongside Conor Dwyer, Townley Haas and Ryan Lochte, feels the "fun" has only just started.
"Now I'm looking forward to rest of the week - I am not even halfway done yet," he said. "I was doing the math and there is maximum of seven races left so we have got our work cut out the next couple of days."
Phelps will begin his quest for a 22nd Olympic gold medal on Wednesday with preliminary heats for the 200m individual medley, an event he won at the expense of American team-mate Ryan Lochte in London.
He will also swim the 100m butterfly and the 4x100m medley relay as he looks to finish the games with six golds.
"It's remarkable. You know, given not just his age but everything that's transpired since London and before London and the whole totality of that," Phelps' coach Bob Bowman said.
"That 200 fly was really great. I mean, somebody asked me where that ranks and I ranked it number two.
"His first one will always be my favourite, and by that I mean his first 200 fly medal not his first race, but that one was definitely number two."