Houston Astros vs Arizona Diamondbacks Prediction – 7/21/2025

The Houston Astros continue their road trip at Chase Field on Monday night with a game against the Arizona Diamondbacks. Houston arrives having struggled in recent games against division opponents. Arizona has been playing well and will look to keep doing so to help their Wild Card chances. Here, I break this game down from all angles and give you my Astros vs Diamondbacks prediction.

Our Astros vs Diamondbacks Pick

• Pick: Arizona Diamondbacks Moneyline
• Confidence: ★★★☆☆
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Game Snapshot

• Matchup: Houston Astros vs Arizona Diamondbacks
• Date & Time: July 21, 2025, 9:40 PM EDT
• Starting Pitchers: Colton Gordon (HOU) vs Zac Gallen (ARI)
• Stadium: Chase Field, Phoenix, AZ
• Broadcast: AT&T SportsNet SW • AZFS

Key Storylines

• Pitching Form: Colton Gordon has allowed five earned runs over 12 innings in his last two starts. He is 3-2 but has a 4.67 ERA on the year. Zac Gallen has been disappointing this year for the Diamondbacks. He is 7-10 with a 5.40 ERA and the Diamondbacks need something special from him in this spot.
• Bullpen Usage: Houston has a big bullpen advantage going into this game. The Astros are in the top five in bullpen ERA for the season. Arizona is in the bottom five in that statistical category. Barring a major surprise, we should see Houston’s pitching be superior in the late innings.
• Recent Team Streaks: The Astros have lost three of their last four games. All of those games were against division rivals in the Seattle Mariners and Texas Rangers. Arizona has won four games in a row entering this one.

Best Player Props

Betting Trends & H2H

• This game is the first meeting between these teams this season.
• St. Louis and Arizona are only set to play three games during the 2025 regular season. All three of those games will take place this week.
• The Diamondbacks are 26-25 at home this season. The Astros are 24-23 on the road.

Astros vs Diamondbacks Model Projection

Score Projection: Houston 4 – Arizona 5

Win Probability: Houston 45%, Arizona 55%

Final Thoughts

The Astros have a statistical edge with both their starting pitching and their bullpen going into this game. But Zac Gallen has a higher ceiling than any of the pitchers that we expect to see significant action in this game. I expect Gallen to pitch well and for the Astros to win the first game of this interleague series from Phoenix.

Jay Sanin

Jay Sanin is a sports bettor, writer and broadcaster from New York. He is an avid New York Knicks fan and is no longer ashamed to admit it. He is also an avid New York Giants fan, and is very ashamed to admit it. His top sports to handicap are the NBA, WNBA and men’s tennis for some reason. He has watched more UAlbany Great Danes basketball than anyone should consume.