The game was tied 2-2 in the eighth when the Cubs erupted for five runs, ignited when Alfonso Soriano and Dioner Navarro got aboard with one out against Matt Thornton (0-3) and Valbuena sent them both home with a double into the left-center field gap.
Dave Sappelt (4-for-5, two RBI) later added a run-scoring hit and Cody Ramson capped the uprising with a two-run single as the Cubs sent 10 men to the plate during the frame.
Soriano finished 3-for-4 with a solo homer and four runs scored as the Cubs took the make-up contest of a rained-out May 28 game.
Matt Garza (5-1) racked up his fourth win in four starts, stifling the White Sox on two runs (one earned) on five hits over seven innings.
Josh Phegley homered for the Chisox, losers of four straight.