Who is the Diamondbacks' Newest Reliever to be Called Up?

Montes De Oca, 25, originally signed with the Diamondbacks as an international free agent at 22 years old out of the Dominican Republic in December 2021. Over his three-plus seasons in the organization, he's steadily climbed the ladder with a 4.17 ERA with 9.8 strikeouts and 3.2 walks per nine innings pitched.

"A kid that's come up through our academy, he's continued to persevere, and grow, and learn, year-by-year-by-year," said Diamondbacks manager Torey Lovullo. "Put himself in a position with an aggressive fastball, some real good secondary stuff that's coming on to earn this call-up."

The right-hander was a non-roster invitee to big league Spring Training with the Diamondbacks this year. He allowed just one run in 5.1 innings, striking out six in five appearances. While his solid numbers likely impressed the coaching staff, he was reassigned to minor league camp and sent to Reno, where he ended the 2024 season.

Following a short stint on the 7-day injured list, he has spent the entire 2025 season with Reno. In 12 appearances, Montes De Oca boasts an impressive 2.37 ERA in a league where the average ERA is around 5.00. The right-hander boasts a solid 17/4 strikeout-to-walk ratio in 19 innings. He can also provide multiple innings, getting more than three outs in eight of his 12 outings with Reno and giving Lovullo some flexibility on the front side of the pen.

He's primarily a four-seam, sinker, and slider pitcher, with his two fastballs in the 94-98 MPH range. He throws his fastballs (49.8%) and his slider (46.0%) almost equally. The slider is his best pitch, as opposing hitters are batting .129 with a .226 slugging percentage and a 31.6% whiff rate. He's gotten good results on his four-seamer (.231 BA, .308 SLG%, 24.1% whiff rate), but his sinker has been hit hard.

With a fastball, sinker, and slider combination, Montes De Oca's stuff profiles better against right-handed hitters. Looking strictly at just batting averages, this holds true as righties are hitting .200 compared to lefties hitting .241. However, when expanding to OPS, the platoon splits are fairly even at .577 and .581 respectively.

The lack of major platoon splits despite the pitch types is attributed to his slider taking on more of a death ball shape at -2.6 inches of induced vertical break and 2.9 inches of glove-side break. Because of the shape, it plays better against left-handed hitters than a typical right-handed slider would. It may also serve as a reason why he has a better strikeout-to-walk ratio against left-handed hitters (8:1) than right-handed hitters (9:3).

Against right-handers, he'll rely on his sinker and slider combination. The sinker is more of a pitch-to-contact offering while the slider is his main swing-and-miss pitch. Against lefties, he trades in his sinker for more four-seamers while relying on his slider as his primary secondary pitch. The four-seam/slider combination generates more swing-and-miss against left-handed hitters (32.1% whiff rate) than his sinker/slider combo to righties (18.4%).

It comes as no surprise that the Diamondbacks promoted Montes De Oca. He would have been eligible for the Rule 5 Draft after the season and was an obvious candidate to add to the 40-man roster in November. In addition to solving that issue, they will get a firsthand look at how the right-hander will perform in the big leagues.

Most likely, he'll start in low-leverage situations so the team can give him a soft landing. How he performs will likely determine what kind of role he has in the future. Montes De Oca projects somewhere between a middle reliever to a setup man who faces primarily right-handed hitters long-term.