Sunday afternoon, Shohei Ohtani returned to the mound for the first time in nearly two weeks. He was very good against the Mariners until the bottom of the seventh, when he failed to retire any of three batters. Still, that partial inning couldn’t spoil the appearance, and Ohtani’s ankle seemed like it must’ve been perfectly fine. To fast-forward here, I’ll note that Ohtani made very quick work of Mitch Haniger in the bottom of the second. Let’s watch that.

The first pitch, a called strike:

The second pitch, which was called a strike on appeal:

And the third pitch, for the putaway:

I’m not sure Haniger ever stood a chance. And if you watch all that quickly, maybe nothing new stands out. Yeah, Ohtani’s fastball has plenty of zip. And he might also throw the best splitter in the world. The fastball there is good, and the splitter there is good. Pay special attention to the second pitch, though. That’s a slider. That’s not a new pitch for Ohtani — people have drooled over that pitch since before he ever crossed the ocean. But Ohtani, on Sunday, leaned more heavily on his breaking balls. For the first time, he succeeded without using the splitter as a crutch.

Brooks Baseball classifies the splitter as an offspeed pitch. Meanwhile, sliders and curves are breaking balls. So, here is Ohtani’s pitch mix by start:

Ohtani just used the most breaking balls, especially against opposing lefties. Lefties had seen mostly fastballs and splitters. Why might Ohtani have gone this way? Because it was working for him. Here’s a plot that’s similar to the one above, except this time showing whiffs:

Through Ohtani’s first four starts combined, his breaking balls registered five swinging strikes. Sunday alone, they registered nine. I’m going to skip almost right past the curveball, but I’ll show you one clip while I’m here:

Ohtani showed the Mariners 11 curveballs, after he’d previously thrown a total of 10. It’s definitely a functional fourth pitch, that expands Ohtani’s velocity range. It’s good to see Ohtani believing in the curve more, but I want to get to the slider, because I think that’s the real story. For the first time in five starts, Ohtani threw his slider with command. Before, he had a slider. Sunday, he had a quality slider. The difference, I think, is dramatic.

Most right-handed pitchers want to throw their sliders low. Many of them want to throw their sliders low and to the glove side. Through the end of April, among righties, Ohtani had the very lowest rate of low sliders thrown. He had the very lowest rate of low and glove-side sliders thrown. He had the highest average slider location, and, even worse, he had the highest average two-strike slider location. Not every single Ohtani slider was intended to be down and off the plate, but far too many Ohtani sliders were backing up on him. Ohtani had been leaving sliders up, often by mistake. Sunday, that problem almost disappeared.

I think this is best understood visually, so I grabbed a couple plots from Texas Leaguers. On the left, Ohtani sliders from his first four starts. On the right, Ohtani sliders from Sunday:

The change there is impossible to miss. Against the Mariners, Shohei Ohtani figured out his slider, shifting them down and to the glove side. Ohtani could throw the slider for a called strike:

But he could also bury it:

And he could make it work against lefties:

We already knew that, by movement, Ohtani could have a quality slider. Now he’s started throwing them well, or at least, he did in one game. It could be that has something to do with the fact that Ohtani pitched to Rene Rivera for the first time, instead of Martin Maldonado. It could be that has something to do with the idea that Ohtani’s blister might be healed. Or it could be that Ohtani is just getting increasingly comfortable with the different seams, as opposed to those he worked with in Japan. I mean, by this point, it’s been months, so maybe that’s unlikely. I’m not sure. But all I care about are the end results, and we just saw a good slider and a consistent slider. For Ohtani, that’s going to be important.

While his fastball is obviously fast, it doesn’t have that much of a swing-and-miss profile. Ohtani’s fastball doesn’t rise all that much, so it probably won’t pile up the whiffs. The splitter is very clearly fantastic, but hitters might also try to eliminate it, figuring it generally ends up below the zone. As a fastball/splitter pitcher, Ohtani could be very good, but he’d be in trouble in games where the splitter is getting away from him. If the slider is going to be there — and, for that matter, the curveball, too — that makes hitting all the more complicated. Ohtani would have more options, and hitters would be more on the defensive. Ohtani, in short, would have a full, complete repertoire. Like he did at his best in the NPB. This isn’t a difficult thing to understand; Ohtani’s better when he has another quality pitch.

Maybe the breaking balls were always going to come along eventually, but now we’ve finally seen them. That’s a meaningful step. Perhaps part of the reason Ohtani was successful against the Mariners was because the hitters kept on expecting to see more splits, but that’s exactly the function of a bigger arsenal. You get to be less predictable, and you give hitters more to think about. A pitcher with three or four pitches has more ways to get guys out than a pitcher with two pitches. It can make a pitcher more effective within a start, and it can make a pitcher more effective in subsequent starts against the same lineups. This is all fundamental, so I’ll stop typing. You all understand the point.

Shohei Ohtani was billed as an ace-level starter with four good pitches. To say nothing of the hitting, of course. That’s the other half of it. In Ohtani’s fifth major-league start, he threw four good pitches for the first time. One start isn’t exactly a pattern. It’s too early to call this a trend. But if Ohtani now has it all working, well, I shouldn’t need to tell you what’s going to happen.