Lefthanded hitters destroyed Reds' righthander Luis Castillo last season. But after changing how often he uses his pitches, Castillo is on the verge of a breakout 2019 campaign.

Next week is a big one for Reds’ righthander Luis Castillo. On Monday, he’ll take the ball against the mighty Dodgers, with Clayton Kershaw making his season debut on the other side. On Saturday, he’ll face off with the Padres, a lineup suddenly packed with powerbats up and down the order. The stakes for Castillo go beyond the two starts, though. Castillo could take another huge step toward his long-expected breakout if he handles these two potent lineups.

Castillo has been excellent through three starts, allowing two runs on five hits in 19 2/3 innings, striking out 25 and walking eight. That translates to a 0.92 ERA and 0.66 WHIP to go along with a 35.2% strikeout rate. Castillo’s ground-ball rate is at 57.1%, and he’s holding hitters to a 13.5% hard-hit rate. Make no mistake, Castillo has been one of the dominant pitchers of the season’s first few weeks.

What’s behind Castillo’s surge this season? He’s still throwing the same four pitches—four-seam fastball, two-seam fastball, slider and changeup—and his velocity is in line with career norms. But he’s altered the usage of his four offerings, cutting the two-seamer’s profile while significantly increasing his reliance on the changeup. The jump in usage to 30% from 26.4%, taken with the pitch’s performance this season, goes a long way toward explaining why Castillo is threatening to reach another level.

Lefties crushed Castillo a season ago, lighting him up to the tune of a .289/.351/.530 slash line with 18 homers and 22 doubles in 351 plate appearances. In other words, lefties hit at an MVP pace against Castillo in 2018. While he did lean on his changeup against them, throwing it 34.5% of the time, he also offered his two-seamer more than 20% of the time to lefties. They raked against it, hitting .392 with a .671 slugging percentage and six homers. Add in their .318 average, .671 slugging and eight homers against his four-seamer, and it was clear that he’d need to change something this season when he lacked the platoon advantage.

To do that, Castillo has cut his two-seamer usage against lefties by nearly half, while upping his changeup usage to 36.8%. The results speak for themselves. Castillo has faced lefties 35 times this season, holding them to a 1-for-29 line with 16 strikeouts against five walks. The lone hit was a single, giving them a .034/.200/.034 slash. It’s all thanks to the changeup.

Among Castillo’s 16 strikeouts of lefties, 13 have come with the changeup as the third strike, and 12 of those have been swinging strikes. Castillo’s 29 whiffs with his changeup lead the majors, and he has the highest whiff rate with the pitch among all starting pitchers. It appears Castillo has harnessed his breakout pitch.

For confirmation, let’s go to no less an authority than last year’s NL MVP and continued wrecker of pitcher’s dreams, Christian Yelich.

This is the pitch for Castillo. The stuff has always been there, but without a changeup he fully trusted, he was too hittable for lefties. That’s no longer the case. It’s worth noting that the only hit he has given up to a lefty this year has been on a change. They’re 0-for-9 against his other offerings as the action pitch, with two strikeouts and two walks. His slider has a 21.5% whiff rate against lefties, while the two-seamer’s whiff rate is up to 10.5%. Not only is the change a nasty offering on its own, it has made the other pitches in his repertoire better because of how they all work in concert.

Indeed, look at how Castillo is now able to use the change and two-seamer in conjunction. He didn’t back them up until his most recent start, a seven-inning, zero-run, two-hit, eight-strikeout domination of the Marlins. In the fifth inning of that game, J.T. Riddle stepped into the box for his second plate appearance of the game. On a 2-2 count, Castillo threw him a two-seamer that just missed the zone down.

Riddle showed impressive discipline by laying off that pitch. However, Castillo now had him set up for the changeup. Watch as he identifies what he thinks is another two-seamer, realizing too late that what he’s really getting is a filthy change.

Castillo is set to see some dangerous lefties on Monday, with Joc Pederson, Corey Seager, Cody Bellinger and Max Muncy all likely to start for the Dodgers. If he handles that lineup, especially those four hitters in it, we’ll have even more reason to believe that Castillo’s breakout season has arrived.

And now, just for fun, how about one more gratuitous changeup whiff GIF. Sorry, Travis Shaw.