Fowler's two-run triple in the fourth inning capped a three-run outburst that erased an early 1-0 deficit and put Colorado ahead to stay.
His sacrifice fly in the fifth put the finishing touches on a four-run fifth that broke the game open for the Rockies, who evened their three-game series at Coors Field.
Nicasio (6-4) settled down after yielding a run in the first inning, allowing three hits and two walks over five innings. The right-hander struck out three.
Cubs starter Carlos Villanueva (2-6) was lit up for seven runs on nine hits over four innings.
Luis Valbuena smacked a solo homer and finished with two RBI for Chicago.