Carter hit two-run homers in the third and fifth innings against Brandon Morrow, raising his spring training total to four. He also hit into a run-scoring forceout in the first.
"I don't really think about hitting home runs," Carter said. "I just try to make contact, and whatever happens, happens. ... As far as timing and the swing, this is best I've felt this year."
Houston's starting outfield likely will have Justin Maxwell in center and Rick Ankiel in right. The 26-year-old Carter was acquired from Oakland on Feb. 4 in the trade that sent Jed Lowrie to the Athletics.
"Early in the spring, it looked like Carter's timing was off a little and the pitchers were ahead of the hitters," new Astros manager Bo Porter. "As you an see, the hitters are starting to catch up. We knew once his timing got down, he has power to all fields and he's very capable of doing what he did today consistently."
Maxwell doubled and tripled off Morrow, who gave up seven runs -- six earned -- and seven hits in 4 2/3 innings.
"I've never had an opening day (job) other than the minor leagues, so it's definitely exciting," the 29-year-old Maxwell said.
Maxwell has 27 home runs in 534 major league at-bats over parts of four seasons, the first three with Washington.
"The way you get comfortable is when you have that experience of playing every day," he said. "You get familiar with the ballparks, you get familiar with the pitchers that you face and then you start making your adjustments within that. That's definitely the way to establish yourself at the big league level."
He hit .229 with 18 homers and 53 RBIs for the Astros last year.
"Just getting a chance to play, being able to showcase myself, I hadn't had that opportunity before," he said. "I'm just looking to get better and trying to improve my game every year, if not every day."
Houston's Bud Norris allowed three hits and struck out five in six innings, giving up consecutive sacrifice flies by Anthony Gose and Rajai Davis in the third. Erik Bedard followed with one-hit relief, striking out five in three innings.
Houston optioned RHP Paul Clemens, OF Robbie Grossman, LHP Dallas Keuchel, OF Jimmy Paredes and INF Jonathan Villar to Oklahoma City (PCL).The Astros reassigned LHP Sergio Escalona, RHP C.J. Fick, OF Che-Hsuan Lin, C Carlos Perez and RHP Josh Zeid to their minor league camp. ... Houston RHP Philip Humber, a strong candidate to be in the Astros' rotation, is to pitch a simulated game Monday.