PHOENIX -- When he was rehabbing from injury during the 2021 season, D-backs right-hander Zac Gallen made sure that he took care of what he needed to do from a physical standpoint. But looking back afterward, he realized that he didn’t focus enough on being mentally ready to pitch when he returned.

When he was placed on the injured list May 31 with a right hamstring strain, Gallen vowed this time would be different. He was determined that when he was physically ready to pitch again, he’d also be mentally ready as well.

"I challenged myself to not fall into that trap," Gallen said.

The results of his work over the last month at the team’s Salt River Fields facility were on display Saturday afternoon as Gallen dominated the A’s for six scoreless innings in the D-backs' 3-0 win at Chase Field.

"I didn't want to come back here and be caught off guard,” Gallen said. "I tried to lock it in from one of the first few days I was really there. I was mentally preparing to pitch. I was treating it like Spring Training where I was getting ready to pitch on Opening Day, not just coming back from an injury."

It seems a subtle difference, but for Gallen it was an important one.

Maybe that’s why Gallen’s stuff was so sharp right from the first pitch. His four-seam fastball came out hot, as he averaged 95.2 mph with the pitch, the highest mark that he’s recorded in his career, besting a 95.1 mph average on June 17, 2021.

"I had a really great conversation with him yesterday about how he utilized his days,” D-backs manager Torey Lovullo said. “He did not waste a day or a moment of his rehab. I know he has 95, 96, 97 mph in the tank, I’ve seen it before, but the way he was commanding it, the way he was just getting after it on Day One … it inspired me and I know it inspired that dugout today and gave us a really, really good, refreshing feeling.”

Gallen suffered a strained right hamstring six pitches into his May 30 start against the Mets, but because the injury was to his lower body he was able to keep throwing during his recovery. That allowed him to not have to go through an extensive injury rehab assignment and instead pitch in a pair of simulated games at Salt River Fields.

Gallen allowed just one hit on Saturday, a bloop single by Brent Rooker in the first inning, and one walk, striking out seven and throwing 77 pitches. It was Gallen’s fifth career start of 6+ innings and one hit or fewer, and his second of 2024.

"I felt like I had everything going,” Gallen said. “Didn’t throw any cutters but fastball, changeup, slider, curveball felt like they were all there for the most part. Felt like the things I've been working on delivery-wise had kind of clicked."

Watching Gallen pitch the way he did certainly had Lovullo and the team’s front office dreaming about what the rotation could look like when they get the rest of their injured players back.

Fellow starters Merrill Kelly and Eduardo Rodriguez have missed all or a large chunk of the season. Rodriguez could be back sometime after the All-Star break, while Kelly’s timeline could stretch into August.

Both could provide big boosts to the rotation and help a D-backs team that has struggled to gain traction this year following last season's exciting run to the World Series.

"I know that Merrill and E-Rod were watching and I'm sure they're excited to continue their progression to step into this venue, in this type of an atmosphere and help us win games,” Lovullo said. “That's what it's all about."