Concerns about Duffy's physical state are based in logic. He has endured Tommy John surgery, and he was troubled last season by an injured rib cage.
But Duffy's velocity, which sat around 95 mph in his short stint, relieved some concerns.
As Duffy explained after the game, he simply didn't have it.
"Everything was working fine in the 'pen," he said. "I was kind of pulling my slider. My changeup was fine. I was locating it down. I really just didn't do my job today. I left the bullpen hanging and put the boys in a bad position."
Duffy went one inning, then faced five hitters in the second without recording an out. He left trailing, 4-0, in the shortest non-injury start of his career.
"I just didn't have my stuff tonight," he said. "It's a weird feeling and I haven't had it for a long time, but it will happen again at some point in my career. I'll just try to keep those starts few and far between.
"I'm not in any way shape or form happy with what I did tonight."
Duffy wasn't even sure when he knew he had nothing working.
"You never really think, 'Do I have it or don't I have it?' But I knew I was off," he said. "I threw a slider to [Brandon] Moss and it was like eight feet outside. You don't have it every time you go out there.
"I'll have confidence that I'll do my job the next time I go out there."
Jeffrey Flanagan is a reporter for MLB.com. Follow him on Twitter at @FlannyMLB. This story was not subject to the approval of Major League Baseball or its clubs.