Giants catcher Buster Posey was struck in the helmet by a 94 mph fastball in the first inning and forced out of the game, a frightening moment in San Francisco's 4-1 victory Monday against the Arizona Diamondbacks in its home opener.

An update on the 2012 NL MVP's condition was planned postgame, the team said.

Taijuan Walker's 0-1 fastball with two out in the first inning sent the Gold Glove catcher immediately to ground. Athletic trainer Dave Groeschner sprinted toward the plate and manager Bruce Bochy was right behind. Posey got up on his own but exited the game, with Nick Hundley entering to pinch run and stay in the game as catcher.

Walker (1-1) was booed at the conclusion of the inning, when he came up to bat and at every other opportunity by the AT&T Park sellout crowd of 42,129.

Matt Moore (1-1) struck out five in eight impressive innings. Mark Melancon got his second save.