Ryan Lochte believes he will need a perfect performance in order to defeat Michael Phelps in Thursday's 200 metre individual medley at Rio 2016.
Phelps comfortably beat American team-mate Lochte in Wednesday's semi-final and will go for a 22nd gold and 26th overall Olympic medal in the final.
Lochte was second behind Phelps in the same race at London 2012 and, despite owning the world record in the 200IM, knows he has little room for error against the most decorated Olympian of all time.
"I love racing against him [Phelps]. He's the toughest competitor and racer I've ever had to go up against. We bring the best out of each other," Lochte said.
"It's going to take a perfect performance in order to beat him just because of how tough of a competitor he is. He won't give up, and that's awesome.
"That's why he brings out the best in me and hopefully I do the exact same for him."
While Phelps and Lochte have a fierce competitive rivalry, they continue to enjoy a strong friendship away from the pool
Lochte added: "Whenever we go up on the blocks, we're always trying to win. That's just our competitive instinct that we have.
"But you know, win or lose, at the end we're still good friends and we don't let swimming decide that."