"It was nice to get back out there that late in the game," he said. "I was really happy to contribute to what was a great performance by everybody."
Duffy entered Wednesday's game to begin the bottom of the ninth with the score tied. He gave up a single, then retired the next three hitters, two with strikeouts.
Jose Altuve led off the Houston 10th with a single, but Duffy struck out the next hitter and picked Altuve off first. A walk and another single put runners on first and third, but Duffy struck out L.J. Hoes to end the inning, giving him four strikeouts in two innings.
"That's why we brought him up," manager Ned Yost. "He's a kid who possesses a 97 mile per hour fastball. Let him experience the Major League game from the bullpen side. We think his benefit to our organization (long term) is going to be as a starter. Right now he's a reliever. He steps on the mound, doesn't have any fear and he attacks."
The Royals called up Duffy from Triple-A Omaha last Saturday and he pitched that night, retiring all seven batters he faced.
"They just said they needed an extra arm in the 'pen," said Duffy, who had never been a relief pitcher in his pro career. "I happen to have good stuff [Wednesday] night and was really lucky [Yost] gave me the opportunity. It gave me a whole lot of confidence. After what happened, I realize if I execute my pitches, it's going to get done because of how hard I throw. If I can keep my slider and get my changeup back, it's going to be a lot of fun."
Duffy's rehab from Tommy John took 16 months. It can be a mental grind as well as physical.
"You can't wonder [if you'll ever get back]," he said. "It's a mental battle. Surgery is down to a science. The rehab and how you approach it is debatable. If you try to be optimistic throughout, which is nearly impossible, and try not to think about what will happen and won't happen, the rehab goes faster.
"It was long and tedious. We had the right guys in the training room to keep me on track. I don't have any soreness after starts anymore. The only thing I really feel is fatigue. That comes from a year of not pitching."
After a rough Spring Training, Duffy began the season in Omaha. He made one start, pitching six innings and throwing 94 pitches, before getting the call from the Royals.
"It would have been really hard for me to win a spot [in the rotation]," he said. "I didn't have a good spring. I worked on holding myself accountable for the pitches I threw, and not making excuses. I'm never good at spring. Not a lot of people are. But I was tremendously bad.
"I feel better now than I've ever felt. I was so happy to get back. When you have it, and it's taken away from you, you realize how lucky you are to have it. You have to sit and watch for 16, 18 months, you realize what you've got. From now on, it's keeping it where it's at."