The Park City racer waited for the start at the junior cross-country World Championships in Saalfelden, Austria, and when he finally heard the gun sound, he went to step down and missed the pedals.
"I just blew my start," he said. "I went from the front to a ways in the back. I knew I just had to start pedaling as hard as I could."
Many of the most talented junior racers from across the globe were now ahead of Swenson. After falling behind early, he slowly began to stalk them.
He made his moves, passing racers one by one, before he eventually cracked the top 10.
"I think without that stumble, he probably would have had an easier race for second," said coach Tom Noaker. "It's hard to come back. At the World Championship level, you make an early mistake and 30 people pass you. Those aren't Intermountain Division kids. Those are the fastest kids in the world."
Swenson said rather than panicking following a rough early go, he just did what he knows how to do, and that's race.
"With three laps to go, I caught the French guy who was in fifth, so that was a good moment for me," Swenson said. "The next guy (fourth place) was like 20 seconds ahead of me and I was closing in on him, but I couldn't quite get ahead of him at the end."
Despite that nightmarish start, Swenson claimed fifth in the World Championship race. Park City's own biking prodigy said, all things considered, the fifth-place finish is sweet.
"I wasn't so happy about (the start) and I'm not sure why it happened," he said. "I just think I was nervous and just missed my pedals. I hadn't had that happen all year.
"I was really happy with how I finished. Everything went well except for the start. I didn't flat or have any bad crashes; I had a few bobbles, but never slapped really hard anywhere. I was happy with that and that I rode a clean race."
Not many have the luxury of saying they're top five in the world in anything and Swenson now has a top-five finish on the world's biggest stage.
Noaker, who has been Swenson's coach since he was 12, said he is extremely proud of just how far the 18-year-old has come in their six years working together.
Asked if he saw Swenson's innate abilities from the beginning, Noaker said, "From about age 13, yeah. The first year you coach kids, you never know. He was the youngest kid on the team at the time. In the second year he showed up and was dragging the rest of the team around with him, which was extraordinary. By the time he was 14, he had the goods."
While Swenson spent a majority of his summer participating on the World Cup circuit, Noaker and his protégé were able to keep in constant contact through Skype video chats. Going into the World Championships in Austria, Noaker said Swenson was in perhaps his most impressive physical shape since the two started working with one another.
"It was obvious to me that (his shape) was the best all year," he said. "Our plan worked from a training standpoint, he just had a little bobble. For me, we just try to cut off mistakes before he might make them."
The World Championships race was Swenson's last official race as a junior rider. Two days later, he participated in an Eliminator race, a mixture of 200 pros, U-23s and juniors zip around a 500-meter loop. The top 32 racers qualified from the field of 200 and Swenson said he finished 70th. The field was so tight, he trailed the time-trial leader by about 10 to 12 seconds, and the final 32 by five seconds.
Swenson said he's appreciated his time as a junior racer and enjoyed all of his accomplishments, but now that he'll be racing on the U-23 circuit, he couldn't be more excited for the opportunity.
Noaker said Swenson's initial challenge at the next level will come with just racing against more seasoned riders who have more mileage and race experience.
"He's going to be the 18-year-old in a five-year-difference age group," he explained. "That's going to be a tough step to make. It won't be like he's mixed in with a bunch of pros at U-23, but with that being said, the race distances increase by a full lap. Even at these Worlds, the juniors were putting lap times in faster than the U-23s. (Keegan's) response was, 'Yeah, I could have done another lap.' I don't think that endurance factor is an issue for us."
In the coming weeks, Swenson will be competing in cyclecross races in Las Vegas, Nev., and Fort Collins, Colo.
Noaker reiterated that he's not concerned about Swenson's ascent into the U-23 group, saying, "If I say go fast, he'll go fast and that's easy for him to do."
As evidenced by his storming back in Austria.