"I'm excited to have this opportunity here, either to play first base or outfield or DH, whatever I can do to just play every day," said Carter, who hit 16 home runs in 67 games for Oakland last season.
Carter is among at least eight Astros outfielders competing for starting spots.
"That's why we're giving everybody an equal number of at-bats," manager Bo Porter said. "We want to give everybody an opportunity throughout the first three weeks."
Houston starter Bud Norris struck out one and walked one in three innings, allowing Descalso's two-run single in the second.
With Houston trailing by two runs in the ninth, Brandon Laird homered off Victor Marte leading off, his second home run in two days. Rene Garcia singled with one out and, after a throwing error by shortstop Ryan Jackson, pinch-runner Delino DeShields scored on Marte's wild pitch.
NOTES: Cardinals manager Mike Matheny was not with the team because he has flulike symptoms. ... Jose Veras, Houston's likely closer, pitched a 1-2-3 fourth with a pair of called strikeouts in his final appearance before joining the Dominican Republic for the World Baseball Classic.