PEORIA, Ariz. -- At this time last year, Scott Servais’ impression of George Kirby’s path to the Majors was “that this could take him a while.” Little did the Mariners’ manager know that Kirby would later execute the type of in-season adjustments that showed the makings of an established star, not an eager rookie.

Kirby copycatted pitches from his teammates, learned a more robust arm-care routine in order to take on more than double the innings from the year prior and, at times, overpowered MLB’s best teams.

“That's like unheard of in our game,” Servais said. “For a young player to be able to make those kinds of adjustments and then to incorporate into his arsenal as quickly as he was against the best players in the world, like, that’s special. And I didn't know he had that ability.”

Servais’ references mostly centered on the two-seam fastball that Kirby added in late July after toying with it in bullpen sessions. This spring, he’s part of the trend of splitter-throwing starters -- along with Logan Gilbert and Robbie Ray -- unveiling the new pitch during his Cactus League debut on Saturday, a 7-1 loss to the Rockies.

Kirby “threw one good one” and “the other was to the backstop,” chalking the split up to “50-50” as he dusted offseason rust. Overall, he surrendered four runs (two earned) on four hits and a walk with one strikeout over 1 1/3 innings.

“I’ve got some work to do, that's for sure,” Kirby said. “But I think when I get going, I think it'll be a really good pitch. I kind of just throw it like a heater and it just falls off the table more vertical, and then I still have my changeup, which is more horizontal.”

Kirby threw six different pitches last year -- the two- and four-seamer, curveball, cutter, slider and changeup, per Statcast. Among 148 arms who threw at least 1,500 pitches last season, only Kirby, Chris Bassitt and Jameson Taillon threw six different pitches at least 8 percent of the time. And only Shohei Ohtani threw seven different pitches in total.

“George can pick up a baseball, turn it and throw it and it’ll do whatever he wants it to do,” Ray said. “The guy is super talented.”

Unlike Gilbert, who’s throwing his split with changeup behaviors, Kirby’s is “more like a heater.”

“A little more deception, something with a little more depth to get more swings and misses, some weaker contact,” said Kirby, who began throwing it this offseason without consultation, but rather by admiring videos of splitters.

“I was like, ‘I like that -- I’m going to try it,’” Kirby said so simplistically, underscoring his ability to avoid patterns and predictability. He also blended a skill of limiting damage -- going 14 straight starts without allowing a homer -- and not giving up free baserunners, with a 4.1 percent walk rate that ranked fifth in MLB (min. 130 innings). Kirby did so despite not debuting until Mother's Day after losing the battle with Matt Brash last spring for Seattle’s No. 5 rotation spot.

“He was pissed that he didn't make our team,” Servais said. “Sometimes, that's all a player needs, to go down there, light a little fire and then he shows up and he ain't going back.”

This spring, Kirby is a lock and the final Mariners starter to debut, a by-design effort to -- like Gilbert -- ease him into the regular season. Between the Minors, the Majors and the postseason, Kirby threw 164 2/3 innings last year, capped by seven scoreless frames in Game 3 of the AL Division Series, the first postseason game in Seattle since 2001. Also like Gilbert, who reached a new innings highmark, Kirby said he “was definitely tired” once he went home for the offseason.

But, just as impressive in Servais’ eyes as Kirby’s ability to add pitches was the proclivity to arm care and constantly maintaining his routine between starts.

“I think just really being diligent during the week with my recovery, more so than ever,” Kirby said. “I think just throwing every five days and throwing 100 innings more than I did last year, just had to really focus on that.”

More than the rest of Seattle’s rotation, Kirby’s spring is as focused on building arm strength. Last season, he had a 3.39 ERA and 109 ERA+ (league average is 100) while holding hitters to a .264/.299/.393 (.693 OPS) slash line.

Above all, the Mariners trusted the rookie in their biggest moments of the season -- illustrating that maybe the best is yet to come.