Karstens struck out eight, while allowing one walk and just four hits, all singles. The Astros got to second base just twice against Karstens, once when Jose Altuve stole second and once when Scott Moore singled and advanced on a balk.
The Pirates scored one run in the second when Garrett Jones doubled and Casey McGehee knocked him in with a Texas Leaguer near the right field line for a double of his own. In the third, Karstens singled, Neil Walker hit a ground-rule double, and Andrew McCutchen walked to load the bases. Jones brought home Karstens with a sacrifice fly. Bud Norris hit McGehee to load the bases again, but struck out Pedro Alvarez to end the inning.
The Pirates put two men on to start the fifth but didn't score, in part because Drew Sutton got picked off second. But it didn't matter -- Karstens had given the Pirates more than enough to win.
If the Bucs can keep getting strong outings like this from Karstens, that would be huge, as it would give the Pirates another dependable starter to go along with James McDonald and A.J. Burnett.