Javier Baez paced Chicago's offense early in the game, singling and scoring on Jeimer Candelario's first-inning triple before doubling home a fifth-inning run.
Kyle Schwarber, making his first appearance in left field since tearing two ligaments in his left knee during the third game of the 2016 regular season, played four innings and twice grounded out to second base.
Trailing, 3-0, the Giants began their comeback with three fifth-inning runs.