Clarkson, 37, and Garner, 47, relived their win on the NBC game show during Wednesday's episode of The Kelly Clarkson Show.
Clarkson and Garner were partnered for the special Red Nose Day episode of Hollywood Game Night, which raised funds to help end child poverty. The pair said they got "annoyingly competitive" as they teamed up against Kristen Bell, Sean Hayes, Kenan Thompson and other stars.
"She was so competitive right off the bat," Clarkson told the audience.
"It makes me sweat just thinking about it," Garner said. "I haven't even watched it because I feel like it would give me heart palpitations."
"I get annoyingly competitive at games," Clarkson added.
"I do, too," Garner agreed. "It's not that cute."
Clarkson showed footage of herself and Garner yelling answers and celebrating on Hollywood Game Night.
"We might come across a little crazy, but we won and you want us on your team," Clarkson said.
Garner said she enjoys playing games, including One Night Ultimate Werewolf and Code Names, with her kids. The actress is parent to 13-year-old daughter Violet, 10-year-old Seraphina and 7-year-old son Samuel with ex-husband Ben Affleck.
Clarkson, meanwhile, is parent to 5-year-old daughter River Rose and 3-year-old son Remy with husband Brandon Blackstock. She featured her daughter in her "Broken & Beautiful" music video, released in April.