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

OAKLAND -- Mitch Spence is enjoying a strong start to his Major League career, particularly since moving into the A’s rotation on May 17, as he has a 3.12 ERA through his first five outings.

Spence's ability to mix in five different pitches -- cutter, slider, curveball, sinker, changeup -- to keep hitters off balance has been a key to his success. One pitch, however, stands out above the rest: his slider.

Entering Tuesday, Spence's slider had generated a horizontal break of plus-9.7 inches compared to the league average (sliders thrown at a similar velocity and release point). Among 300 qualified Major League pitchers, that number is second-highest in the Majors, just behind Padres right-hander Joe Musgrove's plus-10.3 inches.

“Since high school and college, I’ve always been able to spin a breaking ball really well,” Spence said. “I’ve always kind of honed in on the slider. The biggest thing between a slider and a curveball for me is the separation between the curveball is really vertical, and the slider is really horizontal. I’ve always kind of worked on trying to make the slider have a lot of horizontal. I get a lot, but it’s not something I’m chasing.”

Sunday against the Blue Jays was an example of how effective Spence’s slider can be. He allowed two runs on five hits in seven innings and retired the final 16 batters he faced. Spence threw his slider for 34 of his 89 pitches and induced 18 swings and six whiffs with it.

Any contact the Blue Jays did make off Spence's slider was mostly weak. Of the seven sliders they hit in play, the average exit velocity was 87.2 mph.

“I just feel like it’s one of my better swing-and-miss pitches,” Spence said. “I also feel like I command it really well. To righties, it’s probably my best swing-and-miss pitch. To lefties, I feel like I can land it early. It’s just something that I can show. Usually, when I throw a backdoor [slider] to a lefty, it’s a take, so it lands as a strike.”

With a Run Value of 4, Spence’s slider is performing as his best pitch this season and one of the better sliders across baseball. He’s thrown nearly as many sliders (320) as cutters (324) this season, and has limited opposing hitters to a .238 batting average against the slider.

If Spence is going to continue succeeding throughout the rest of his rookie campaign and beyond, it’s most likely going to come on the strength of his slider.

“I don’t think it’s a pitch I’m trying to throw more,” Spence said. “It’s just when you’re behind in counts, it’s a pitch I know I can throw for a strike, and it’s either going to get weak contact or be a swing and miss. It’s just a pitch I have a lot of confidence in.”