Hernandez, making only his second career start in left field on Monday night, clubbed a two-run home run off Jameson Taillon in the fifth inning to send the Astros to a 3-1 win over the Pirates at PNC Park. Bregman added a solo blast to center in the ninth.
Hernandez, 23, is hitting .281 with three homers and six RBIs in 10 games in the big leagues.
"I just try to be patient at home plate, try to make some adjustments," Hernandez said. "The past couple of games, I was swinging at pitches out of the zone. I'm just trying to do the best I can -- see the ball and try to hit it hard and do some damage."
Taillon dominated the Astros through four innings and had allowed just one baserunner. A.J. Reed led off the fifth with a walk and Hernandez sent a 3-1 fastball over the left-field wall to break a scoreless tie.
"We had a hard time figuring out Taillon," Astros manager A.J. Hinch said. "No one had seen him and he had good stuff. Really good arm, really good breaking ball and decent changeup. Threw a ton of strikes and I was surprised he even walked Reed before the home run. We got the big swing when we needed it and got a tack-on run at the end, which always makes you feel comfortable, with Bregman's homer. Hernandez, a big night."
Hernandez spent last season at Double-A Corpus Christi and hit just .219 with 17 homers and 48 RBIs, but wowed the big league staff when he came over from Minor League camp as a Grapefruit League fill-in player this spring. He then went out and hit a combined .307 with 28 doubles, 10 homers and 53 RBIs in 107 games at Double-A and Triple-A before earning a callup two weeks ago.
"I'm surprised at how balanced he's become," Hinch said. "A year ago, he was struggling in Double-A and was all over the batter's box. He was chasing a lot of pitches, his zone control wasn't as good. Our development staff did a really good job of honing him in and getting him in the strike zone, and getting him very comfortable in the batter's box where he's not jumpy, he's not sliding through the hitting zone.
"He's staying with his approach and recognizing pitches at a much better level than we expected, given how his career track had been. The tools have always been there. He's always had some upside and certainly is showing it."
Brian McTaggart has covered the Astros since 2004, and for MLB.com since 2009. Follow @brianmctaggart on Twitter and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.