Gonzalez's homer in the opening inning was his 32nd of the season and gave him 100 RBIs. He's in prime position to challenge for the NL Triple Crown, leading in average (.340), taking over the top spot in RBIs and vaulting into a third-place tie with Joey Votto and Mark Reynolds in homers.
The player teammates refer to as "CarGo" also showed off his arm as well, racing over in left to scoop up a ball, twirl and fire a strike to second to nip Brandon Phillips as he tried to stretch a single into extra bases in the fifth.
Led by Gonzalez's breakout season, the Rockies have climbed back into the thick of the wild card race. They're now 4½ games behind Atlanta.
Cincinnati dropped its third straight, but still maintained a six-game lead over St. Louis, which lost to Milwaukee 4-2.
Chacin (8-9) has been stellar down the stretch, turning in his fourth straight outing in which he has surrendered two earned runs or less. The rookie right-hander allowed two runs and six hits, struck out five and walked one.
Matt Belisle pitched a scoreless seventh before Rafael Betancourt gave up a two-out homer to Jonny Gomes in the eighth that made it a one-run game. Huston Street worked the ninth for his 16th save in 20 chances.
Johnny Cueto (12-5) was back with the Reds after missing a few days to attend a family emergency in the Dominican Republic. The righty lasted six innings, giving up four runs — three earned — and seven hits.
Miguel Olivo drove in what proved to be the decisive run with an RBI double in the sixth. The inning was set up when the normally sure-handed Phillips booted Seth Smith's two-out grounder to second.
A hustling Votto paved the way for a two-run fourth inning.
With two outs and two on, Ramon Hernandez hit a grounder to third baseman Melvin Mora, who tried to beat Votto to the bag instead of throwing to first. Votto was safe by a step and Drew Stubbs followed with a two-run single just over the head of shortstop Troy Tulowitzki, cutting the deficit to 3-2.
Gonzalez got the Rockies going in the first inning, hitting a drive to left after Eric Young Jr. and Dexter Fowler led off with singles.
An inning later, with runners on second and third and two outs, the Reds elected to intentionally walk Gonzalez — a ploy that paid off as Tulowitzki grounded out to end the threat.
NOTES: Reds OF Jay Bruce (right side strain) took 50 swings in the indoor batting cage and is scheduled to take batting practice Wednesday. He probably won't play in the series with the Rockies, but may over the weekend against Pittsburgh. ... RHP Edinson Volquez was recalled from Class-A Dayton on Tuesday and could start Saturday. ... Rockies INF Ian Stewart (strained oblique) is expected to play rehab games Wednesday and Thursday in rookie Casper. ... LHP Jeff Francis (shoulder soreness) threw a light bullpen session Tuesday. ... Gonzalez extended his hitting streak to a career-best 15 games.