SEATTLE -- Most every Major League team has a great unknown, a player who could be a difference-maker if things go right, but questions loom as to whether that potential will play out over the long haul.

For the Mariners, that man is Yusei Kikuchi.

The free-agent signing from Japan has looked impressive this spring and pitched very well in Thursday’s 5-4, 12-inning victory over the A’s in Tokyo. But as with any rookie, there are questions.

Kikuchi isn’t your typical rookie, given he’s 27 years old and has a strong track record in Japan. But he will face adjustments once Major League hitters have a chance to see his stuff, and he’s also adapting to the rigors of MLB, where pitchers typically start every fifth game as opposed to once a week in Japan.

Toss in the acclimation to a new culture, new environment and new city, and there are reasons to wonder how Kikuchi might fare. But the early signals are that the newest Mariners import is equipped to handle all those challenges well.

"I thought Kikuchi threw the ball outstanding,” manager Scott Servais said after the southpaw's debut in Tokyo. “With all the family and friends looking on, the first time out, he was awesome.”

Now the challenge will be to build on that first start. Kikuchi threw a lot of pitches in his opener. He rode the adrenaline through four scoreless innings, but tired in the fifth as he gave up three hits and two runs -- including an unearned run that crossed after he left the game -- as his pitch count reached 91.

The impressive fastball-slider combination bodes well, but he’ll need to continue to adapt. And the Mariners understand that will take time.

“I thought Yusei adjusted very quickly to our Spring Training and what we’re about,” Servais said. “The thing that really stood out for me, when we acquired Yusei, we knew he had good stuff. We knew he threw hard, had a good curveball and slider, but what was really impressive to me was his ability to continue to throw strikes and really attack the strike zone. Like all pitchers, he’s going to give up a few hits, but he did not back off.”

It will be the long haul that shows exactly what the Mariners have from their new man from Japan. He’s already learned to adjust to the slicker balls that MLB uses as well as to the different workouts and training methods, which are far different from Japan.

“Yusei is a learner,” Servais said. “That’s how he’s wired. He wants to learn the Major League game as quickly as he can. The questions he’s asked show he’s very diligent in his work and wants to come up with a routine as quickly as he can to adjust to our game and get the results he’s looking for. I’ve been very impressed with how he’s gone about his work.”

And therein may lie the greatest factor in Kikuchi’s ability to maximize that unknown potential. He wants to be great and he’s embraced the chance to work with his boyhood idol, Ichiro Suzuki, while only further emboldening his desire to succeed and prove himself in the United States.

While Ichiro and Kikuchi are on opposite ends of the age spectrum, one just starting as the other departs, they have similar work ethics.

“The common trait between both these guys is their great respect for the game,” Servais said. “I think it says a lot about Japanese baseball and culture on how these guys prepare and go about their business, which is a great example for all our players. They are the most prepared guys we have and it comes from their upbringing in Japanese baseball culture. We are very fortunate they’re built that way. They’re very structured and don’t deviate from their plan. And it’s worked for both of them.”