Michael Phelps won his first event on return from an eight-month ban from competition, claiming the 100 metres butterfly title at the Mesa Arena Pro Swim Series.
Up against long-time rival Ryan Lochte, Phelps touched the wall first in Arizona in a time of 52.38 seconds - ahead of Lochte (53.11secs).
Tom Shields was third in a time of 53.18secs.
"I did what I had to do," said Phelps, who declared the Rio Olympics as one of his targets on Wednesday.
"Afterward, I can say my stroke didn't feel good, I needed one less stroke, I needed to kick more, the breakout on my turn was bad.
"I could pick apart the race 100 different ways, but just getting in the water and racing was something I was looking forward to."
Despite the loss, Lochte welcomed back Phelps to the pool.
"I'm just glad he's back," Lochte said.
"He's the hardest racer in the world. He'll go toe-to-toe with you in any event, and I love that, because it's a challenge whenever you go up on those blocks with him."