Mier was 2-for-4 with three RBIs as Class A Advanced Lancaster beat High Desert, 8-6, on Wednesday night.
With the JetHawks trailing in the third inning, 2-0, Mier cut the deficit in half with an RBI single in his second at-bat. After flying out his third time up, the Astros' first-round pick in 2009 gave Lancaster its first lead of the game with a two-run double to left field.
"I was just battling," Mier said. "I think it was one of those days where I had to grind my at-bats out and find a way to put the ball into play. I just tried to give our team the opportunity to win and the ball bounced our way tonight."
After starting the season 1-for-14 in his first four games, Mier has seemingly found his hitting stroke, batting .364 with seven RBIs over his last eight California League games.
"Really just trying to be aggressive and put together good at-bats," the 21-year-old shortstop said. "I'm trying to make all of them count and whatever I do in the previous at-bat I'm trying to let it go."
Mier ended the 2011 season in Lancaster, where he batted .233 with 23 RBIs in 55 games. In three seasons since being drafted, the California native is batting .244 with 16 homers and 137 RBIs.
"The past few years I've gotten away from what I've done early and I try to find my swing in the middle of the year," Mier said. "Every day I'm just trying to go back out and have the same at-bats. I'm just trying to stay on an even path and not getting too high or too low. Just make sure my swing and approach stays the same every day."
Telvin Nash, the Astros' No. 10 prospect, slugged his seventh homer of the year, tying Toledo's Brad Eldred for the Minor League lead.
"He's pretty impressive," Mier said. "The California League is known for being a hitters' league, but all his homers have been impressive especially the one tonight. It might have been the farthest one I've ever seen. When he gets ahold of one, it's pretty impressive."
Julio Morban was 4-for-5 with two RBIs and finished a triple shy of the cycle for the Mavericks.