Buster Posey hit a two-run homer off new Arizona closer Addison Reed in the ninth inning and the San Francisco Giants rallied from four runs down to beat the Diamondbacks 9-8 on Monday night.San Francisco Giants' Pablo Sandoval turns around after striking out against the Arizona Diamondbacks during the first inning of an opening day baseball game, Monday, March 31, 2014, in Phoenix.Arizona Diamondbacks' Miguel Montero, left, scores a run as San Francisco Giants' Buster Posey, right, drops the ball during the fourth inning of an opening day baseball game, Monday, March 31, 2014, in Phoenix.San Francisco Giants' Madison Bumgarner throws a pitch against the Arizona Diamondbacks during the first inning of an opening day baseball game, Monday, March 31, 2014, in Phoenix.Arizona Diamondbacks' Aaron Hill runs out on the field during player introductions prior to an opening day baseball game against the San Francisco Giants, Monday, March 31, 2014, in Phoenix.