Jordan Schafer homered and scored three runs as the Houston Astros defeated host San Francisco 3-1 on Thursday to drop the Giants three games behind the Arizona Diamondbacks in the National League West.

Pitching on three days rest, Astros starter Henry Sosa (1-2) earned his first major league win against his former team. Sosa gave up one run on four hits over six innings.

Mark Melancon worked around Carlos Beltran’s leadoff single in the ninth inning for his 14th save of the season.

J.D. Martinez had two doubles and improved to 7-for-16 against the Giants this season. The Astros had four stolen bases while snapping a four-game losing streak.

San Francisco, which has lost 18 of its last 26 games, fell to 8-53 when trailing after seven innings.

Giants starter Ryan Vogelsong (10-4) allowed three runs over 7 1/3 innings and lost for the third time in his last four starts.