"We were representing Europe. They have this celebrity match thing before the main event," he explained to host Ellen DeGeneres. "Niall and I, we won our match. We beat Michael Phelps and Nick Jonas."
The Fifty Shades star said he has over 20 years of experience, while Horan has youth on his side.
"I'm okay. I should be better. I've played for over 20 years, but it's tough with time and kids. I wish I was better," Dornan said.
"[Niall's] younger than me, obviously, so he's got that. I've got 14 years on him or something," he added.
Horan said in a tweet Sept. 26 that he had fun with Dornan at the tournament.
"Had a great laugh playing alongside Dornan against Michael and nick yesterday @rydercup," he wrote. "We won our game and played some good stuff .. now it's over to the boys of @RyderCupEurope to take that trophy back. Cmon Europe."
The One Direction singer later said the tournament was an unforgettable experience.
"Well that was one week I'll never forget. So happy for everyone @RyderCupEurope," he wrote.
Dornan is known for playing Christian Grey in the Fifty Shades movies, which concluded with Fifty Shades Freed this year. He will star in the new film Robin Hood with Taron Egerton and the HBO movie My Dinner with Hervé.