What are the key mistakes that hurt Zac Gallen and the Diamondbacks on Thursday?

Zac Gallen looked exactly like Arizona’s stabilizer early on with efficient pitch sequencing and weak contact. His efforts in the beginning suggested he could neutralize a lineup anchored by Shohei Ohtani, Mookie Betts, and Freddie Freeman. Then came the fifth inning, a case study in how quickly margins collapse against championship-caliber teams.

Zac Gallen gives up run in fifth inning:

Three of the Dodgers’ first four hits that inning came with two strikes. That’s not just bad luck; it’s execution failure. Two-strike pitching demands precision, either chase-inducing off-speed or elevated fastballs out of reach. Instead, Gallen left pitches hittable. Max Muncy’s single set the tone. A slow infield knock by Teoscar Hernández extended the pressure. Then, Andy Pages delivered the swing that flipped the night with a 400-foot homer.

Strategically, the Diamondbacks were already thin. Without Corbin Burnes and Merrill Kelly, Gallen isn’t just a starter; he was asked to be the tone-setter. That amplifies every mistake. The fifth inning wasn’t about his talent; it was about finishing. For D-backs fans, the takeaway is both sobering and clarifying, as against elite teams, dominance isn’t measured in innings won, but in moments closed. Arizona proved it can build a lead. The next step, one that defines contenders, is learning how to suffocate momentum before it turns.