"For sure, he wanted the chance to do it," Yost said. "The score was at a point where we could do it and provide him an opportunity. My mindset was that if two guys got on [in the ninth] we would go and get him."
Duffy came within one out of a complete game, but he left after a season-high 110 pitches in the Royals' 6-2 win over the Phillies on Saturday night.
Duffy gave up seven hits, walked none and struck out eight in his longest outing in the bigs.
"Obviously, it's cool to finish a game because those guys in the bullpen have picked me up so many times when I've been inefficient," Duffy said. "So if I got the opportunity to, might as well try to save another day.
"So that was kind of my mindset. A complete game would be cool, but those guys have been taxed by me a lot in my career. So my best way to pay them back is trying to keep them from pitching."
How did Duffy convince Yost to give him a try?
"I just told him I wanted to finish it," Duffy said. "He gave me an opportunity, I'm really grateful for it."
All of Duffy's eight strikeouts came on either changeups or curveballs.
"My changeup still wasn't there as much as I wanted it to be," Duffy said. "But it was there enough. I was losing a lot arm-side. I think probably the best changeup I threw today was probably the last pitch of the game for me. But he poked it through the infield, so it is what it is."
Duffy had another reason to celebrate Saturday: He got his first Major League hit and RBI on a push bunt that popped over the pitcher's head in the five-run second inning.
Duffy said he wasn't sure he tried that push bunt on purpose.
"I think I tried to take [the bat] with me to first," he said. "I don't know. Your guess is as good as mine. It got the job done.
"I looked into the dugout and they were telling me to bunt. I'm obviously not here to hit, so it just worked. It just worked."
First-base coach Rusty Kuntz secured the baseball for Duffy.
"It's been five years in the bigs," Duffy said. "You think I'd probably would have had a hit by now. But that was my first one [after 10 at bats]. I'll take it."
Jeffrey Flanagan has covered the Royals since 1991, and for MLB.com since 2015. Follow him on Twitter @FlannyMLB. This story was not subject to the approval of Major League Baseball or its clubs.