Can Zac Gallen Maintain D-backs' Momentum vs Astros?

The Arizona Diamondbacks can't let up now.

May 28, 2025; Phoenix, Arizona, USA; Arizona Diamondbacks pitcher Zac Gallen reacts in the fifth inning against the Pittsburgh Pirates at Chase Field. Mandatory Credit: Mark J. Rebilas-Imagn Images | Mark J. Rebilas-Imagn Images

The Arizona Diamondbacks have forced their way back in the race, sweeping the St. Louis Cardinals in a brilliant showing to begin their second half. They'll look to continue that upward trajectory as the Houston Astros come to town for three games. First pitch Monday is set for 6:40 p.m.

While a second-straight sweep may not be on the table, another successful series would go a long way towards forcing general manager Mike Hazen out of a seller's mentality.

But it'll be up to right-hander Zac Gallen to give his team a chance Monday.

Arizona Diamondbacks vs Houston Astros Pitching Matchups

RHP Zac Gallen (5.40 ERA) vs LHP Colton Gordon (4.67 ERA)

Gallen was not able to continue his own personal turnaround his last time out, giving up six runs in five innings to the Angels in Anaheim.

Prior to that start, he had allowed just one run over 13 innings while striking out 19. The Diamondbacks need that version of Gallen back, for good, if they want to keep rolling into contention.

If Gallen has sharp fastball command, he may be in line for another quality start. If not, Monday may be another blowup waiting to happen.

The Astros will turn to left-hander Colton Gordon. Gordon, 26, has struggled a bit in the rotation, and was even used in a bullpen role in his last appearance.

He gave up nine runs in 10.1 innings in his first two starts this month, but threw a scoreless inning of relief. Gordon has pitched to a 4.67 ERA, but a 4.01 FIP, which suggests he's been the victim of some poor batted ball luck.

He'll work out of the rotation again Monday. Gordon throws a low-90s four-seam and sinker, a sweeper, curve and occasional change.

Gordon has limited walks to an exceptional degree with just a 3.9% walk rate, but has been hit relatively hard across the board.

Diamondbacks vs Astros Lineups

Houston’s in town. https://t.co/k9Xjx1ui6d pic.twitter.com/G2ohCiIcxh

— Arizona Diamondbacks (@Dbacks) July 21, 2025

Ketel Marte makes his official return after being reinstated from the restricted list Sunday. He'll DH and bat leadoff. Corbin Carroll will get his first start of the season in center field, with Randal Grichuk playing right.

Diamondbacks vs Astros Bullpens

The D-backs got quality innings out of their starters and long relievers in their sweep of St. Louis. Anthony DeSclafani was the only reliever to work Sunday, leaving nearly all of manager Torey Lovullo's "High Leverage" options, such as they are, available for the upcoming series.

The Astros had to spend seven relievers in an 11-inning loss Saturday in which closer Josh Hader threw 35 pitches. They used four more on Sunday, including setup men Bryan Abreu and Bryan King on a back-to-back.

Houston's bullpen will be relatively fatigued. Knocking their starters out early could spell success for Arizona in this series.