Norris hits first career homer to give A's walk-off win Sun Jun 24, 2012 8:17pm EDT (Reuters) - A first career home run from Derek Norris gave the Oakland Athletics a walk-off ninth-inning 4-2 victory over the visiting San Francisco Giants on Sunday. Norris, who made his Major League debut last Thursday, came to the plate with two outs and Oakland trailing 2-1 before he slugged a three-run homer for a dramatic win that helped the Athletics (35-38) avoid a three-game sweep. Red-hot San Francisco pitcher Matt Cain allowed one run over seven innings and was in line to win his ninth straight start - something no Giants pitcher has done since 1952 - but the bullpen let the victory slip away. Closer Santiago Casilla pitched the ninth, and allowed singles to Yoenis Cespedes and Brandon Inge prior to the big blast to be charged with the defeat. Oakland starter A.J. Griffin also made his big league debut in place of injured Brandon McCarthy. He allowed a first-inning two-run homer to Buster Posey, the Athletics also scored in the first, but was strong over six innings. Reliever Jim Miller tossed the final 1 1/3 innings to record the win.