'Ultimate success story': Yilber Diaz set to make Diamondbacks debut

When the Diamondbacks first discovered Yilber Diaz, he was selling candy on the streets of Latin America, trying to make ends meet as he looked for an opportunity to pitch.

In February of 2021, the Diamondbacks gave him that opportunity. They signed the 20-year-old Venezuela native as a non-drafted free agent with a signing bonus of just $10,000.

Diaz’s pro career did not start off well. In his first year of rookie ball in the Dominican Republic, Diaz posted a 5.13 ERA in 26 1/3 innings with more walks than strikeouts.

His fastball sat in the low 90s, and his command was poor. The Diamondbacks considered releasing him.

Three years later, Diaz is touching 99 with improving command and two quality secondary pitches. He is among the best pitching prospects in the Diamondbacks’ organization. On Monday night, he will make his first major-league start against the Atlanta Braves.

“His grit, his mindset, his work ethic got him over the hump, and [he is] the ultimate success story,” Diamondbacks farm director Shaun Larkin told PHNX Sports. “It’s an all-encompassing moment for player development as we watch him make his debut tonight. It’s really cool.”

Diaz, 23, has a 4.03 ERA in 76 innings this year split between Double-A Amarillo and Triple-A Reno, with 105 strikeouts compared to 38 walks. Since being promoted to Reno on June 11, he has a 3.27 ERA in four starts.

In his most recent Triple-A outing on July 1, Diaz assembled perhaps the best pitching performance of his career. He tossed six no-hit innings with two walks and 13 strikeouts. At one point, he struck out seven consecutive batters.

Yilber Diaz (@Dbacks No. 16) was on another level tonight!

🔥 Career-high 13 strikeouts across 6 hitless innings
🔥 Tied the Triple-A @Aces single-game K record
🔥 Fanned 7 batters in a row pic.twitter.com/gu3jsbglUm

— MLB Pipeline (@MLBPipeline) July 2, 2024

“He just overwhelmed Triple-A hitters,” Larkin said. “The fastball command was great. He was blowing guys away with the fastball and slider. We had some of our advanced people in there.

“It was a good day for those guys to be in there watching him do his thing. It was a special night.”

When Diamondbacks starter Jordan Montgomery hurt his knee in a bullpen session last weekend, Diaz’s name came up as a potential replacement. Diamondbacks manager Torey Lovullo said that Diaz’s most recent dominant outing solidified the club’s belief that he was ready for the majors.

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Yilber Diaz’s pitch arsenal

Diaz has a three-pitch mix that includes a four-seam fastball, slider and curveball.

In his four Triple-A starts, Diaz threw his four-seamer 53.7 percent of the time, his slider 33.7 percent and his curveball 12.6 percent. Diaz’s four-seamer averaged 95.9 mph and topped out at 98.9 mph. The slider and curveball averaged 84 mph and 79.4 mph, respectively.

All three pitches proved to be effective in Triple-A. Opposing hitters hit .250 with a .446 slugging percentage and a 25.8 percent whiff rate against Diaz’s four-seamer — all strong numbers in the hitter-friendly Pacific Coast League.

In Diaz’s outing on July 1, he induced 15 whiffs on the four-seamer alone.

Here is an example of a particularly good one at 98 mph:

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While Diaz’s fastball can be dominant, his best pitch is arguably his slider. PCL hitters have hit just .118 against it with an eye-popping 54.5 percent whiff rate.

Here is one from his start in Salt Lake City on June 19:

Diaz’s curveball is more of a show-me pitch than a swing-and-miss offering, but opposing batters hit just .222 against it in Triple-A.

With hitters gearing up for Diaz’s high-octane four-seamer, the curveball can be an unpleasant surprise.

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In the past, there has been widespread speculation that Diaz would be best suited to pitch out of the bullpen. However, his command has improved enough in recent months to warrant further consideration as a starter.

Earlier this season in Double-A, Diaz experimented with a changeup. He did not throw it in Triple-A, and likely will not throw it in the majors for now.

Even without a secondary pitch that tails away from left-handed hitters, Diaz has more than held his own against them this year. Lefties hit just .200 against him in Double-A and .212 in Triple-A.

Larkin said that Diaz can get away with a three-pitch mix because his curveball acts as a neutralizer against lefties when he lands it for strikes. Larkin also pointed out that Diaz’s slider can function as a cutter when thrown in on lefties’ hands, and that Diaz’s fastball has enough on it to beat barrels and avoid hard contact, regardless of the handedness of the hitter.

On Monday, Diaz will face a tall task against a Braves lineup that just belted nine home runs in a three-game series against the Philadelphia Phillies.

“He’s got the stuff to compete at the major-league level,” Larkin said. “Now, it’s about execution.

“Either way it goes,” Larkin added, “he’s gonna learn a lot from it.”

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Top photo: David Calvert Photography/Reno Aces