"We've talked about him being among the elite pitchers in the National League and he proved it again today," Maddon said.
The outing wasn't without a rough spot. Arrieta walked two batters in a 22-pitch first inning before settling down.
"I was a little too fine early in the game," he said. "I recognized it. There were some close pitches, some checked swings, some balls that maybe could've gone either way."
Maddon said he almost expects a moment in every start when Arrieta is "out of sorts."
"In the early part of the game, he'll go through a moment where things just aren't right and then he'll find his rhythm and flow and things take off," Maddon said. "I don't get too freaked out by it because I've seen it before."
Sunday marked the sixth double-digit strikeout game of Arrieta's career, and he's now given up two or fewer runs in six consecutive starts, the third longest active streak in the Major Leagues.
"I'm never satisified," Arrieta said. "I feel there's always room to get better and especially on the finer details of this game. That's what I try to do every week."
"He's just figuring everything out right now," Maddon said. "I hate to tell you, but there's more in the tank there, and another level. As he gets more self awareness and is able to deal with all these weapons that he has, he'll get better."
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings. You can follow her on Twitter @CarrieMuskat and listen to her podcast. This story was not subject to the approval of Major League Baseball or its clubs.