Perhaps nobody in the Los Angeles Dodgers‘ front office watched Yoshinobu Yamamoto pitch in Japan more often than Galen Carr, the longtime scout who now serves as vice president of player personnel.

Last summer, at an Orix Buffaloes road game north of Tokyo, Carr watched Yamamoto unleash a pitch that took even him by surprise: A mid-90s fastball with arm-side run and sink, a two-seamer — or a sinker, or a shuuto, depending on who you ask — that sharply deviated from the hellacious four-pitch mix that had made him one of Major League Baseball’s most coveted pitchers.

“It was like, ‘Wow,'” Carr recalled. “He didn’t pull that one out of his bag very often.”

Since signing Yamamoto to a 12-year, $325 million deal in December, the largest contract ever given to a starting pitcher, the Dodgers have watched him make an assortment of monumental transitions — to a new ball, a new mound, a new country, a new league and now, basically, a new repertoire.

Yamamoto is still in the second full month of his major league career, and yet he has already evolved into a different pitcher, his pitch mix increasing from four to six.

The four-seam fastball, the rainbow curve and the darting splitter continue to be his bread and butter. The cutter remains an intermittent weapon. Over his past four starts, though, Yamamoto has also unveiled a two-seamer and a slider against right-handed hitters. It’s yet another dynamic for the 25-year-old right-hander whose early numbers — 5-2 with a 3.51 ERA and a 5.31 strikeout-to-walk ratio despite an ugly major league debut — are beginning to justify the hype he carried with him from Japan.

“[He’s] more than just a rookie,” Dodgers first baseman Freddie Freeman said. “This is a guy who’s never been in the United States. He’s learning the language, he’s learning Major League Baseball, he feels like every time he goes out everyone expects him to throw a complete-game shutout. There’s a lot on him. For him to go out there and do what he’s been doing these first two months, I think it’s special.”

Yamamoto occasionally flashed the two-seamer and slider in Japan, but as Dodgers assistant pitching coach Connor McGuiness noted, “he honestly just didn’t need it.” Yamamoto won three consecutive Pacific League MVPs from 2021 to 2023, during which he posted a 1.42 ERA in 557 2/3 innings and mostly survived on three pitches.

The Dodgers’ initial focus was on making his transition as smooth as possible, which meant placing him on something close to the once-a-week schedule he was accustomed to in Japan and keeping his repertoire tight. Any tinkering would wait.

“When he first came over to us, a big point of emphasis was just making sure he was comfortable — getting used to the American ball, getting used to our catchers, just kind of how we go about things, the different talent level of lineups that he’s facing,” McGuiness said. “So he was really showcasing the main three early on. And the more and more we got to know him and he started to feel much more comfortable with his delivery, it just opened him up to really showcase his talent and skills to be able to do different things.”

Yamamoto allowed five runs and recorded only three outs during his major league debut in South Korea on March 21. He recovered admirably, posting a 1.64 ERA over his next six starts, but an ominous trend began to emerge: Right-handed hitters were faring well against him, slashing .281/.311/.491 through May 1. Against his fastball and curveball, those numbers jumped to .350/.357/.650.

Yamamoto had the splitter and, to a lesser extent, the cutter as put-away pitches against lefties. But he needed more options against righties. The two-seamer could bust them in on their hands; the slider could tail away and make them chase. In recent starts, both pitches have been consistent weapons. Yamamoto barely used them while facing a lefty-loaded Cincinnati Reds lineup on Sunday, but he threw a combined 25 two-seamers and 20 sliders in starts against the Miami Marlins, San Francisco Giants and Arizona Diamondbacks from May 7 to May 20, the vast majority to right-handed hitters.

They went a combined 2-for-13 with four strikeouts against those pitches. In that stretch, their overall slash line against Yamamoto went down to .233/.250/.442.

“He’s always had all of these pitches,” McGuiness said. “It was just a function of once his delivery is in a good spot to really showcase them in a game.”

The slider — thrown in the mid-80s, about six ticks slower than his cutter but with significantly more depth — first made an appearance against the D-backs on May 1. Yamamoto threw three of them, one of which badly fooled Christian Walker for a strikeout. When the D-backs saw him again on May 20, Yamamoto unleashed 11 two-seamers and 10 sliders, both season highs. Three of those sliders drew strikeouts, including one to the left-handed-hitting Joc Pederson.

“There’s tremendous aptitude there, and he’s got a great feel for the baseball,” D-backs manager Torey Lovullo said. “I think it’s just the awareness and the creativity that he has. And he’s probably trusting some coaching. He saw that there was a need to change shapes with a couple of his pitches and has transitioned really well. The fact he’s been able to do it as fast as he has is impressive, but not surprising.”

Dodgers hitters were blown away early in spring training by Yamamoto’s stuff and command. A handful of starts into his major league career, Dodgers manager Dave Roberts saw a pitcher who “got tired of being mediocre” and honed in on the details of his mechanics because of it. Easing into his major league career, Roberts said, “wasn’t good enough for him.” Effectively incorporating two additional pitches so soon is a perfect example.

Yamamoto had been throwing two-seam fastballs in bullpen sessions since the early part of spring training but waited until the mechanics of his delivery were sound before unleashing the slider, a pitch historically troublesome on elbows. The shapes of those pitches are ever-evolving, as is Yamamoto’s transition to the big leagues. He has continually worked on not leaking his four-seam fastball out over the plate, an issue that has led to a 48.5% hard-hit rate. Over time, McGuiness said, he’s “learning what a good miss means” and how it can enhance his sequencing.

He still has a lot to learn, but he’s doing it quickly.

“As we got to know him, that’s something that really stood out — his aptitude, his thoughtfulness, the questions he asked,” Carr said. “You could tell he was a real student. I mean, there’s so much intent with every throw that he makes. When he’s playing long toss and you watch him, he’s focused and intentional on every single throw he makes. So if those are your building blocks and you combine that with superior coordination, athleticism — it’s pretty exciting to feel like you can probably ask him to make some adjustments and he’s going to be OK.”