"The first one was kind of an out-of-body experience," Duffy said after the game. "Kind of blacked out for a second."
Duffy entered the game at third base in the fourth as a defensive replacement for Marwin Gonzalez and caught a Rougned Odor pop fly to lead off the inning for his first Major League putout.
The Pacific Coast League MVP led off the fifth with the groundout and batted two more times, drawing a four-pitch walk in the sixth and striking out in the ninth.
"Obviously, I dreamed of it since I was a kid, so to get that out of the way was nice," he said. "There's just a lot of thoughts running through your head. I tried to look out to center field and take it all in for a second. It's definitely one I'll remember for the rest of my life."
Manager A.J. Hinch said that Gonzalez -- who's been dealing with pain in his right wrist after a hard slide last week -- didn't re-aggravate the injury and was removed as both a precaution and as a way to get Duffy a taste of September baseball.
"It's unfortunate to make his Major League debut [in this type of game], but a great accomplishment for him to get to the big leagues and a great reward for him for how well he played [in Triple-A]," Hinch said. "He'll forever be able to call himself a big leaguer."
Chandler Rome is an associate reporter for MLB.com.