The Phillies' secret weapon for the postseason isn't exactly a secret anymore -- his MLB debut was too electric.

Orion Kerkering, the team's No. 7 prospect, took the mound for the first time on Sunday and immediately showed the playoff-caliber stuff the Phillies were hoping for when they called him up.

The 22-year-old right-hander made it immediately clear that he can help load up the reigning National League champion's October bullpen.

Here's a closer look at Kerkering's nasty stuff.

The sweeping slider

This is the main attraction. Kerkering threw 12 pitches in his MLB debut against the Mets. Ten of them were sliders -- or, sweepers, as Statcast is going to classify the pitch moving forward, since it has ridiculous horizontal movement.

You have to be one confident 22-year-old to throw your breaking ball over 80% of the time in your first Major League outing. And, well, Kerkering's confidence sure looks warranted.

Kerkering's sweeping slider averaged 87.4 mph with 16.5 inches of horizontal break in his debut. Six of the 10 that he threw were called or swinging strikes. He struck out two of the three batters he faced, both on sweepers, and both of those sweepers broke 20 inches.

This is the cool part about what we saw from Kerkering: Very few Major Leaguers throw a pitch in the slider family -- either a traditional slider or a sweeper -- with the combination of speed and movement that Kerkering possesses.

Hardest sliders/sweepers with 10+ inches of break
Matt Brash -- 88.8 mph / 11.6 inches of break
Graham Ashcraft -- 88.3 mph / 13.2 inches of break
Kyle Bradish -- 88.1 mph / 12.5 inches of break
Orion Kerkering -- 87.4 mph / 16.5 inches of break
Calvin Faucher -- 87.2 mph / 10.7 inches of break
Jordan Hicks -- 86.8 mph / 12.4 inches of break
Griffin Jax -- 86.7 mph / 13.5 inches of break
Wil Crowe -- 86.5 mph / 12.5 inches of break
Alex Cobb -- 86.2 mph / 11.0 inches of break
Corbin Burnes -- 86.1 mph / 12.1 inches of break
George Kirby -- 86.1 mph / 11.3 inches of break

If you look at that list, though, Kerkering's movement number stands out from the rest. It turns out that no one who throws a slider or sweeper at Kerkering's velocity level also generates as much horizontal break as he does.

Compare Kerkering to a typical big league pitcher throwing some type of slider or sweeper. The average MLB slider in 2023 is 85.2 mph with 5.7 inches of horizontal break. The average MLB sweeper in 2023 is 81.9 mph with 14.2 inches of horizontal break.

A traditional slider is harder with tighter movement; a sweeper gets big break but comes in slower. That is the nature of those pitches, and why Statcast has a distinct classification for each.

Then you look back at what Kerkering is throwing. He's really messing with the model.

Is it more a slider or more a sweeper? Kerkering is spinning up sweeper movement at hard slider velocities. (In fact, if Kerkering keeps up his velocity at its current level, he'll be throwing the hardest sweeper in the big leagues.) There are only a few pitchers who can do that consistently -- guys like Brash, or Evan Phillips, or Shohei Ohtani -- and they have some of the nastiest breaking stuff around.

How about this fun fact. Five of Kerkering's 10 sweepers were thrown at 87-plus mph and had 17-plus inches of horizontal movement -- that is, they moved at least the full width of home plate. And then on top of that, both of his sweeper K's fit into that category.

Kerkering is one of only four pitchers in MLB all season with multiple strikeouts on sliders or sweepers that broke the full width of the plate at 87 mph or harder. He's one of only eight pitchers with even a single K on a pitch like that.

Most slider/sweeper K's at 87+ mph with 17+ inches of break
Graham Ashcraft -- 12
Matt Brash -- 6
Griffin Jax -- 3
Orion Kerkering -- 2
Shohei Ohtani, Evan Phillips, Kyle Bradish, Calvin Faucher -- 1

The average horizontal break for a slider or sweeper thrown 87 mph or harder is ¡­ 4.0 inches. The average velocity for a slider or sweeper thrown with 17-plus inches of horizontal break is ¡­ 80.6 mph.

In other words: A normal Major League pitcher can throw either a hard slider or a Frisbee sweeper. Kerkering has both in one pitch.

Even his catcher, the great J.T. Realmuto, took notice: "I don¡¯t know if it's classified as a sweeper or not because it's so hard, but it has that type of movement, that type of horizontal break. It's 88 mph. It's one of the more unique sliders that I've seen in the game."

The 99 mph fastball

Oh, right, Kerkering threw two other pitches that weren't ridiculous sweepers. And those were ¡­ a 99.2 mph fastball and a 99.8 mph fastball.

Yes, Kerkering was sprinkling in a near-triple-digit heater as a "show me" pitch.

His harder fastball, the one that butted up against 100, also ran back 13 inches perfectly onto the inside edge of the plate to start the at-bat against Rafael Ortega, before Kerkering buried him with sweepers.

If Kerkering is throwing pitches like that, he's going to get outs in the playoffs. And he's got the potential to get big outs.