Charlie Morton was doing fine until the sixth, when six of the first seven batters reached base. Five of those runners scored, and by the time Morton had been replaced by Chris Leroux, the damage had already been done.
The Astros also scored three runs in the ninth off relievers Dan McCutchen and Danny Moskos.
Bud Norris pitched seven strong innings for the win, as the Pirates managed only seven hits, all singles. Michael McKenry went 2-for-3.
The Pirates are now 45-42. The first-place Cardinals lost to the Reds Wednesday night, but the Milwaukee Brewers won, so the Pirates are still 1.5 games back of the N.L. Central lead, but they’re in third place, a half-game behind the Brewers.
The Bucs kick off a home series against the Chicago Cubs on Friday.