"I threw a couple of pretty good sliders that [Guzman] swung through and then I just started trying to make the perfect pitch," Duffy said. "I was pumping fastballs and was feeling pretty good, and Choice gets up there and I threw a fastball right belt high and he really slammed it."
Duffy, who lost a rotation spot in competition with Yordano Ventura, has given up six home runs and six walks in 11 innings.
"It's frustrating but we'll get through it," Duffy said.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.