J.A. Happ tossed six strong innings and the Houston Astros erupted in the late innings for an 8-2 victory over the lowly Pittsburgh Pirates on Sunday.

Happ (3-1) allowed two runs and three hits in six innings. The left-hander, who was making his fourth start with Houston since being acquired in the Roy Oswalt deal, struck out five and walked four.

Houston helped him remain unbeaten in three home starts by exploding for seven runs over the last three innings. Chris Johnson homered and Jeff Keppinger drove in a pair of runs for the Astros, who outscored Pittsburgh 48-18 in the three-game series and have won nine straight against the Pirates at Minute Maid Park.

The Astros trailed 2-1 before rallying against Jeff Karstens (2-9) and Sean Gallagher in the sixth. Keppinger tied it with a sacrifice fly and Jason Castro gave the Astros a 3-2 lead with a single that chased Karstens.

Feliz greeted Gallagher by ripping a two-run double to center, giving Houston a 5-2 advantage. Hunter Pence added an RBI double in a two-run seventh and Johnson capped the scoring with a solo homer in the eighth.

Karstens allowed five runs and seven hits in 5 2/3 innings.