PHOENIX -- If you didn't watch the D-backs vs. Cardinals game on Sunday afternoon at Chase Field and instead listened to Arizona starter Zac Gallen describe his outing, you might think it was just an average start.

"I kind of felt like I was grinding a little bit," Gallen said. "Like I was working harder than I really wanted to."

If you think that's hard to reconcile with Gallen's six shutout innings in the D-backs' 5-0 win and series victory, then you don't understand how Gallen approaches his craft.

Perfectionism is one way to describe his approach. Though he'll tell you, he's heard other adjectives used. It's a constant quest for any way to get a little better or find the tiniest edge, so don't expect him ever to be satisfied with a performance.

Gallen's manager and teammates are far more effusive in their praise for an outing like Sunday, especially for his curveball, which started out looking like a strike to hitters only to dive below the zone as they swung over it.

"I think the breaking ball was elite," D-backs manager Torey Lovullo said. "It seemed like he could throw it anywhere at any time. The fastball came out real hot, real aggressive and he established that and then went to work with his secondary stuff."

Gallen faced a real threat in the second when the Cardinals loaded the bases with just one out, but he retired Brandon Crawford and Michael Siani to end the threat.

Given that Cardinals starter Miles Mikolas seemed to have his good stuff as well, getting out of the second without any damage was a lift to the offense.

"Mikolas was really good today and he was gonna make us work," catcher Tucker Barnhart said. "It just felt like the game was on the line to me and I think that he did a heck of a job getting out of there with [no runs]. It's rare to get out of that with nothing. You're trying to limit the damage as much as possible -- try to give up one, not two, not three, whatever the case may be -- and being able to get out of there with a zero is huge."

Gallen finished third in the NL Cy Young Award voting last year and is off to another good start to the season. In holding the Cardinals scoreless for six innings while striking out seven, he lowered his ERA through four starts to 1.64.

"I'll take that," Gallen said of the six shutout innings. "I mean, you guys heard me say a lot last year after a good outing that I didn't feel my best. I think it's just me really just kind of striving, not for perfection, but just for excellence. I know what it feels like and what it takes. Today, I feel like I'm getting really close, honestly. Just things are starting to click a little bit more and I'm able to make the adjustments a little bit quicker."

Gallen was at 90 pitches when Lovullo removed him after the sixth inning. Gallen initially tried to talk his way into staying in the game but relented.

With the D-backs counting on being in a pennant race late in the season, Lovullo wants to make sure his ace is fresh for close games when he wants to push Gallen's pitch count above 100. He discussed this with Gallen during Spring Training, and the manager wants to stick to it.

"I think we learned a good lesson last year," Lovullo said. "When I can clip his innings early, I'm going to do that. He's on board with that, but he's such a competitor that he said, 'I'm good,' but I said you've done enough."