TOKYO — Even Bobby Finke didn’t know he could swim this fast.

But his uncanny ability to find a second gear in the pool — especially in the final 50 meters of a long-distance race — resulted in two surprise gold medals at these Olympics for Finke, a 21-year-old distance swimmer from Tampa, Fla.

Finke, a first-time Olympian, won the men’s 800-meter freestyle on Thursday. On Sunday, he won the 1,500 free. Coming seemingly out of nowhere, the performances left everyone — his opponents, his coaches, even Finke himself — a bit stunned.

“I didn’t know I had these swims in me,” a smiling Finke said Sunday. “When I noticed during the 800 prelims that I was still with the guys, I was just trying to ride the wave and have fun.”

Riding the wave made Finke one of the surprises of the Games. His winning time in the 1,500 on Sunday was 9.05 seconds faster than his top time in the distance this year. Dave Durden and Greg Meehan, the men’s and women’s coaches of the United States team, were asked afterward if they knew Finke was capable of speed like this. They threw their hands up and laughed.

“I don’t think we necessarily saw the performance in the 800 going the way that it went,” Meehan said. “But we certainly saw it coming in the mile. I think everyone in the building knew what was coming down that last 100 of the mile.”

Finke became the first American to win gold in the men’s 1,500 since Michael O’Brien in 1984, then said he hoped his performance would spark more interest in the event — a grueling marathon in a sport where sprinters are often the stars — back in the United States.

“Distance swimming within the U.S. has been relatively weak the past five years,” Finke said. “I hope a lot of younger kids get inspired and come up here and kick some butt, too.”

After his victory on Sunday, Finke said it had felt hard in the opening laps of the race to stay with the lead pack. But once he saw that he was indeed able to keep up with the leaders, Germany’s Florian Wellbrock and Mykhailo Romanchuk of Ukraine, he began to build some confidence.

His plan, at that point, was to “just hold on and sprint my butt off at the end,” he said. The sight of Finke surging ahead in the last lap drew a crescendo of noise from the crowd of swimmers and coaches watching from the stands. That sound only grew as Finke took the lead on his final turn.

“I saw how all three of us were kind of neck and neck, and I knew from my 800 that I had the ability to switch gears for my last 50,” Finke said.

He covered the final 50 meters in 25.78 seconds — more than a second faster than any other split by any other swimmer in the race — and was still pulling away when he touched the wall.

Asked at the post-race news conference what he thought about Finke’s race, Romanchuk, the silver medalist, turned to Finke and said, “I don’t like guys who swim just the last 50 so fast.” And then everyone laughed.