A day after a dark substance -- possibly illegal pine tar -- was spotted under the bill of Kikuchi's cap in a win at Yankee Stadium, all sides kept cool.
MLB issued no penalty or even a statement on the matter Thursday.
"It'll work itself out," Mariners manager Scott Servais said before the series wrapped up.
Yankees manager Aaron Boone said his team looked at the tape and that even though he "had thoughts about it," he wouldn't make them public.
"We'll kind of handle it behind the scenes, how we think it's proper," he said.
Pitchers across the majors are known to use a bit of pine tar to get a better grip; that's not a secret. And hitters are generally OK with that, preferring balls are thrown with control.
For the most part, pitchers keep the sticky substance out of sight. In 2014, then-Yankees starter Michael Pineda was suspended 10 games after umpires easily spotted pine tar slathered on his neck during a chilly night at Fenway Park.
Crew chief Dana DeMuth said Thursday that the umpires didn't see anything under Kikuchi's cap and that no one on either side mentioned it during the game.
"Nobody said a thing," he said. "He wasn't doing anything suspicious. In fact, he kept getting a new ball, and he'd throw the old one out toward the Yankees' dugout. It wasn't like he was trying to hide anything."
Kikuchi held the Yankees to three hits in 7 2/3 innings. The 27-year-old Japanese rookie has a four-year, $56 million contract with the Mariners that could be worth up to $109 million over seven seasons if options are exercised.