Ausmus complained to plate umpire Joe West that Cueto's delivery was illegal and later offered his thoughts to reporters, saying Cueto was stopping in his windup.
"Really, the way the rule reads, you're not supposed to even alter your motion," Ausmus said. "That's the way the rule reads. They don't enforce it. Well, he said if he stops it's an illegal pitch."
Cueto threw a four-hitter in his Kansas City home debut as the Royals beat the Tigers 4-0 on Monday night.
Cueto (1-1) did not allow a runner past second base, struck out eight and walked none. It was his sixth career shutout and second this season.
The Tigers trailed 3-0 after one inning, making it easier for Cueto to get into a rhythm.
"You want to think, 'All right, we've got all game to chip away, so go, go, go,' " Tigers left fielder Tyler Collins said. "It just never happened. Cueto did his job. Today's over, and we're going to start preparing for tomorrow."
J.D. Martinez doubled in the second for the Tigers' only extra-base hit.
"Cueto didn't miss in the heart of the plate too much tonight," Tigers third baseman Nick Castellanos said. "He did a good job of working in and out, up and down, changing speeds, and holding and shaking and quick pitching."
Cueto, who was acquired from Cincinnati on July 26 for three pitching prospects, received a loud cheer as he went out for his warm-up pitches, and the standing ovations grew after every scoreless inning as he walked to the dugout.
Cueto struck out Anthony Gose on three pitches to begin the game as the festive Kauffman Stadium crowd roared with approval. Sluggerr, the Royals' mascot, appeared wearing a Cueto-esque mane of dreadlocks.
When Cueto came out for the ninth, the Kauffman Stadium announced crowd of 36,672 rose in unison with a deafening roar that did not stop until long after he retired Victor Martinez on a fly ball to right fielder Alex Rios for the final out.
"A bunch of us were saying in the eighth inning, 'Just watch how loud this gets when he goes out for the ninth inning,' " said Eric Hosmer, who had an RBI single in the seventh. "It was really cool to see and fun to be a part of it.
"It was pretty fun to see, his first game as a Royal at the K and hear the crowd out there in the ninth inning. It was a fun atmosphere tonight, a different feel tonight, a lot of people excited."
Information from The Associated Press was used in this report.