This story was excerpted from Jordan Bastian’s Cubs Beat newsletter. To read the full newsletter, click here. And subscribe to get it regularly in your inbox.

Matt Swarmer admitted there were some nerves when some of the Cardinals’ big-name hitters stepped into the batter’s box in his last outing. That is when the rookie said it was important to just focus on his plan and concentrate on his catcher’s glove.

“I'm just trying to still pitch to what my strengths are,” Swarmer said. “Yeah, when you see these guys, it's like, 'Wow.’ I just can't believe I'm here.”

Swarmer’s strength is a slider that he has learned to manipulate and mask in a way that keeps hitters in guess mode. That is critical, given that the right-hander relies almost exclusively on a fastball-slider combo, while occasionally showing a changeup just to keep one more thing in the back of a batter’s mind. Through two career starts, Swarmer’s formula has worked.

A week ago, when Swarmer faced St. Louis slugger Paul Goldschmidt for the first time, the righty started him off with a 90-mph four-seamer that moved inside for a ball. On the next pitch, Swarmer went with his bread-and-butter. He spun a slider that initially had a similar path before diving down. Goldschmidt had already committed, but pulled off with an ugly half-swing for a strike.

“It's on the same plane as the fastball and then it kind of disappears,” Cubs manager David Ross said. “You get real fastball swings from hitters. Not like, ‘Oh, there's a slider,’ and I try to adjust my swing. They swing through it.”

Through two starts, Swarmer has generated 23 whiffs out of 53 swings (43.4 percent) against his slider. Hitters have gone 4-for-27 against the pitch with nine strikeouts. And the righty has thrown it 52.2 percent of the time, compared to a rate of 44.9 percent for his four-seamer. The changeup accounts for the other 2.8 percent.

And, as Ross noted, Swarmer’s goal is to make the slider look like a fastball as much as possible. That means throwing it from a near-identical release point.

“Back in the day, I used to get around it a little bit,” Swarmer explained. “Now, I'm just kind of straight over the top. And then I never slow down my arm, either. I make it look just like my fastball coming in.”

Per Statcast, the MLB average vertical release point for a right-handed slider is 5.71 feet, compared to 5.86 for a four-seam fastball. Swarmer’s release point for his slider is extremely elevated (6.75) and nearly the same as his four-seam fastball (6.72). That, combined with a funky delivery with a high leg kick, creates a lot of deception for hitters.

“I'm just trying to always make that look like a strike coming in,” Swarmer said. “Hopefully, hitters are just guessing.”