Even though he leads the National League in victories, Jimenez (18-6), hadn't won since Aug. 4. He snapped a personal four-game losing streak even though he didn't have his usual command of his fastball and struggled through a 123-pitch effort.
He allowed seven hits and matched a season high with six walks, one of them intentional, threw a wild pitch and hit a batter in six innings.
The Reds' lead in the NL Central was cut to six games over St. Louis, which beat Milwaukee 8-6.
Troy Tulowitzki homered, tripled and drove in three runs for the Rockies.
Reds rookie sensation Aroldis Chapman hit 102 mph on the stadium radar gun and struck out Tulowitzki. But the Rockies nicked Chapman for three hits during a three-run sixth that made it 8-4.
After giving up four runs in the third inning, Jimenez stranded 11 Reds through the sixth. The Rockies finally gave him some run support in winning their fourth straight game against division leaders — they just took three from San Diego over the weekend, their first sweep on the road this season.
Tulowitzki broke a 4-all tie in the fifth when he sent a fastball from Bill Bray (0-2) halfway up the left-field bleachers.
In the fourth, Tulowitzki followed NL batting leader Carlos Gonzalez's bases-loaded, broken-bat, two-run double down the right-field line with a two-run, standup triple to left-center as the Rockies quickly erased Cincinnati's four-run cushion.
Jimenez was lifted for pinch-hitter Chris Nelson in the sixth and Nelson singled, bringing on Chapman. His 99 mph heater was stroked up the middle by Eric Young Jr. for an RBI single that made it 6-4.
Dexter Fowler's hard shot knocked down shortstop Paul Janish, whose errant throw to second base allowed Nelson to score to make it 7-4. Ryan Hanigan's passed ball allowed another run across before Chapman tied up Tulowitzki with an inside heater for strike three.
The Reds batted around in the third inning, scoring four times on five hits and two walks. Drew Stubbs scored from third on Brandon Phillips' groundout, Chris Heisey followed with an RBI single and Jonny Gomes added a two-run single to make it 4-0.
Jimenez, who let out a big sigh of relief after striking out Stubbs with his 31st pitch of the inning to strand the bases full, drew a one-out walk in the bottom half of the inning, when the Rockies got all four runs back.
The Reds stranded also stranded the bases loaded in the fourth and the sixth and left runners at the corners in the fifth.
For a while this summer, it seemed like Jimenez would obliterate the franchise mark of 17 wins set by Kevin Ritz in 1996 and tied by Pedro Astacio in '99 and Jeff Francis in '07. But after winning 15 games before the All-Star break, Jimenez had been stuck on 17 wins for more than a month, victimized by poor run support and spotty defense.
In his five previous starts, he was 0-4 despite a 3.00 ERA and he received zero or one run of support in four of those five games.
"I think maybe if you want to get right down to it, we've been trying too hard to get the damn thing for him," Colorado manager Jim Tracy said before the game. "We haven't scored for the guy."
Notes: Gonzalez extended his hitting streak to a career-best 14 games with a first-inning double and finished 3 for 5, raising his batting average to .340.
NOTES: Francis (left arm) threw 48 pitches Sunday at Triple-A Colorado Springs and is slated to join Colorado's bullpen later this week. ... The Rockies called up C Mike McKenry from Colorado Springs. ... The Reds are two wins shy of ending their nine-year string of losing seasons. ... The Rockies began a stretch in which 16 of 22 games are at Coors Field, where they're 13-4 since July 29.