Smith's blast highlighted a seven-run third inning that boosted the American League West-leading A's to a third straight win over the Astros and an eighth victory in 10 games overall.
Daric Barton and Yoenis Cespedes chipped in an RBI each for the winners.
Bartolo Colon (15-6) allowed one run over six innings to gain the decision, yielding five hits while striking out seven.
Houston's Lucas Harrell (6-16) was roughed up for seven runs and seven hits, lasting just three innings.
Brandon Barnes and Jose Altuve provided RBI for the Astros.