The Diamondbacks promoted Diaz from Double-A Amarillo to Triple-A Reno on Tuesday, Alex Weiner of ArizonaSports.com reports.
Diaz is now one stop shy of the big leagues, as he'll head to Reno after punching out 77 batters in 54 innings at Amarillo. While he showcased exceptional strikeout stuff, the 23-year-old went 3-5 with a 4.33 ERA across 11 starts in Double-A this season. He's considered one of the Diamondbacks' top pitching prospects.