The last time he went seven innings was last July 24.
Because of Duffy, manager Ned Yost only had to use Jason Frasor and Brandon Finnegan for an inning each, meaning Yost has his big guns -- Ryan Madson, Kelvin Herrera and Wade Davis -- ready to go for the final three games of the series.
"That was just huge for us," Yost said. "Danny just did a great job against a great lineup."
Duffy gave up one run on seven hits and struck out seven in what was by far his best start of 2015.
"After that first inning, I just kind of settled in," Duffy said. "For whatever reason, I've had really long first innings lately. But I got to the second inning, I started locating pretty well. My changeup is what got me through tonight. And the defense, too."
Duffy was most proud that he was able to spare the bullpen.
"I need to give my team innings all the time," he said. "But [pitching coach] Dave [Eiland] said to me yesterday in Cleveland, 'Hey, we really need to get seven from you.' So, yeah, it's important to go deeper into games. I felt good about that."
Duffy threw 101 pitches, 67 for strikes, and walked just two.
"I'm overall pretty happy and pretty pleased," he said, "but my efficiency has to get a little better at times."
Still, Yost was beaming afterward.
"This is why we think he's a front-of-the-rotation guy," Yost said.
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.