Walker (1-0) allowed three hits in a scoreless inning to pick up the win Sunday over the Marlins.
Walker pitched the sixth inning in his major-league debut, alternating between outs and singles. He stayed on to begin the seventh but was pulled after giving up a leadoff single. Walker pitched to a 0.89 ERA, 0.85 WHIP and 23:8 K:BB over 20.1 innings across 15 appearances (three starts) for Triple-A Sacramento prior to his call-up Friday. He'll likely serve as a low-leverage reliever while he's with the Giants.