Paul, who entered the game in the sixth inning, added a double and a single and scored a pair of runs, while Garrett Jones and Andrew McCutchen each had an RBI.
Charlie Morton (7-3) lasted five innings to improve to 5-0 against the NL Central this season. He allowed three runs on eight hits and two walks while striking out three. The Pirates won their third straight and moved above .500 for the first time since May 9.
J.A. Happ allowed two runs over five innings before being spelled by Enerio Del Rosario (0-1), who surrendered three runs in the sixth to suffer the loss.
Michael Bourn went 3-for-4 and Brett Wallace went 2-for-3 with an RBI for the Astros, who have dropped 10 of their last 12.