D-backs Top 40 Prospects in 2024: No. 6 Yilber Diaz

The young right-hander rocketed his way up to a rather successful MLB debut.

Jul 22, 2024; Kansas City, Missouri, USA; Arizona Diamondbacks starting pitcher Yilber Diaz (45) pitches during the first inning against the Kansas City Royals at Kauffman Stadium. Mandatory Credit: Jay Biggerstaff-Imagn Images / Jay Biggerstaff-Imagn Images

This article is part of a series reviewing the seasons of the top 40 prospects still in the Arizona Diamondbacks system as of the end of 2024.

RHP Yilber Diaz, DOB 8/19/2000, 6'0'', 190

Acquired: 2021 international Free Agent Signing

24-year-old right-handed starter Yilber Diaz has been one of the most promising young prospects in the Arizona Diamondbacks' system for the last couple seasons.

Since he was signed as an international free agent in 2021, he's managed to make a jump in minor league level every year, and has shown notable improvement on a steady basis.

In 2024, he began the year in Double-A Amarillo. He only pitched 54 innings, but somehow managed to strike out 77 batters in that time. He pitched to a 4.33 ERA over 11 starts, a number that is a bit better than it appears in an extremely offense-heavy Texas League.

That earned him a swift promotion to Triple-A Reno in mid-June. Once there, he was hit around a bit in his first few starts, but settled into a rhythm and continued his dominance.

Pitching in another extremely hitter-friendly environment in the Pacific Coast League, Diaz put forward a masterful six-inning, thirteen-strikeout performance on July 1. He allowed just two walks, and no hits or runs in that contest, while splitting nearly evenly between looking and swinging punchouts.

That earned him a look from the MLB club. On July 8, the D-backs selected Diaz's contract, and he made his MLB debut that very night, against the heavy-hitting Atlanta Braves.

Diaz was stunning in his first taste of big-league action. He pitched six strong innings in his debut, allowing one walk and four hits, leading to just one earned run (a solo homer), while striking out five.

His next outing looked quite similar. He went six innings once more, again allowing one run on four hits, but only struck out two. His location was a bit down, and he looked somewhat less efficient, though his results were hard to argue with.

That showing earned him his first MLB win, as the D-backs dominated Toronto 12-1.

Unfortunately, Diaz ran into trouble his next time out. Facing a tough squad on the road in the Kansas City Royals, he was smacked around for nine hits and seven earned runs over just 3.0 innings of work. His ERA ballooned from 1.50 to 5.40.

He then bounced back five days later, pitching five shutout innings against the Pittsburgh Pirates. He only allowed one hit, and struck out seven, but struggled with command, and walked four batters.

A day later on July 29, he was optioned back to Triple-A, where he continued to pitch well for the Aces. He spent a brief stint on the 7-day Injured List from August 7-15, but only stayed the minimum seven days.

Over four starts in August, he never surrendered more than three runs in a game, and pitched a curiously strong start on August 21, where he gave up 10 hits, over 5.1 innings, but only two runs.

But as the calendar turned to September, Diaz began making appearances in relief with the Aces. He pitched four and two innings respectively as a reliever, giving up four runs and striking out six in those six total innings.

As it turns out, the D-backs were hoping to see Diaz contribute to their major league bullpen. On September 12, he was recalled to the majors, and made a trio of relief appearances.

He pitched solidly in that stretch, allowing four runs (three earned) over 8.1 innings of bulk relief, striking out five and lowering his major league ERA to 3.81.

On September 26, he was optioned back down once more, and that sufficiently ended his 2024 campaign. He finished with a very impressive 3.22 Triple-A ERA, and struck out 63 batters in just 50.1 innings with the Aces.

2025 Outlook

Diaz is certainly one of the more MLB-ready prospects in Arizona's system. He's already demonstrated an ability to pitch at the highest level, and his penchant for strikeouts make him an electric arm to watch.

But he did suffer a large drop in strikeout rate during his call-ups. With Double-A Amarillo, he punched out batters at a 12.83 rate per nine innings. With the Aces, it was a still-high 11.26. But with the D-backs, it dropped to 6.04, and his .282 BABIP is not necessarily a sustainable number just yet.

Diaz only throws three pitches. A 60-grade plus fastball that averages around 96 MPH and can touch 98, and a pair of solid secondaries with a low-power slider and curve that range from the high-70s to low-80s.

Where the trouble lies is in his command. His command is low, and he often sprays his pitches, or leaves them in favorable hitting spots. That was on display at times, even in his stronger D-backs starts.

But Diaz's raw potential is quite high. He's still young, especially for a pitcher, and has truly never spent more than half a season at any minor league level, other than the one season he spent in rookie ball in 2021.

It's quite plausible that Diaz will see more major league action in 2025, though whether that will be as a starter or reliever is unknown. That will likely depend most on the state of Arizona's rotation and bullpen.

As of now, he's probably the first man up from Reno if the D-backs were to be in immediate need of a starting pitcher. At any rate, he's poised for a solid 2025 season.

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