Tyler Mahle tossed six scoreless innings for the Reds, who beefed up their bullpen again by acquiring right-hander Mychal Givens from Colorado before the game. Tyler Stephenson and Shogo Akiyama each had two RBIs, and Jesse Winker doubled twice and drove in a run.
The 37-year-old Votto is the ninth hitter in Reds history, dating to 1900, to homer in five straight games. It was his 15th career multi-homer game.
''Homer-wise, this is the best stretch I've been on in a short period of time,'' said Votto, a six-time All-Star who noted he's been through hot hitting streaks before. ''I've never done it with the home run, so it's a little bit of a new experience.''
The 2010 NL MVP launched a 1-1 curveball from Zach Davies deep into the left-field bleachers leading off the second. Votto tagged Cory Abbott for a two-run shot to center on a 3-1 fastball in the ninth, giving him 19 homers this season and seven during his five-game surge.
It's coming at a perfect time for the Reds, who need to get on a roll to close ground on NL Central-leading Milwaukee or a wild-card spot.
''He just continues to be fun to watch and contribute in a big way to our wins,'' Reds manager David Bell said. ''It's really a pleasure and a joy to watch him at the plate right now.''
Mahle (8-3) scattered five hits and walked one in his first win since June 16. The right-hander battled through some deep counts and was helped by sharp defense, including a couple of nifty catches by right fielder Aristides Aquino.
''That was probably the grindiest game I've been a part of,'' Mahle said. ''To end up going six innings, let alone no runs, was incredible.''
Newly acquired relievers Luis Cessa and Justin Wilson followed with a scoreless inning each in their Reds debuts before Ryan Hendrix allowed two runs in the ninth, on RBI singles by David Bote and Ian Happ.
Nico Hoerner and Patrick Wisdom each had two hits for fading Chicago. The Cubs have dropped two straight and seven of 11.
Davies (6-7) was tagged for four runs and seven hits. The wiry right-hander struck out eight but walked four.
Votto's opposite-field shot put the Reds ahead 1-0 in the second.
Cubs manager David Ross has noticed some differences in the left-handed-batting Cincinnati slugger.
''He's changed his stance, taller and hitting for more power to all fields,'' Ross said. ''A breaking ball from Davies there, he takes it to left.
''Right now he's just locked in and hitting for power as much as I've seen him. I've been watching him for a long time and he's in a pretty good place.''
Winker lined a double to the center-field wall in the third to drive in Cincinnati's second run.
Stephenson's long single to the left-field wall in the fifth plated two runs to make it 4-0. Kris Bryant threw out Stephenson at second.
Dillon Maples hit Akiyama with a pitch with the bases loaded in the eighth to force in a run before the Reds scored three in the ninth to pull away.
IN GOOD COMPANY
Other Reds batters to homer in five straight games include current 3B Eugenio Suarez (2018), plus Jay Bruce, Devin Mesoraco, Adam Dunn, Ken Griffey Jr., Johnny Bench, George Crowe and Ted Kluszewski.
PROPPING UP THE 'PEN
The Reds kept adding arms to their struggling bullpen - and signaled they're intent on climbing into the playoff hunt - by getting Givens from Colorado on Wednesday for two prospects, RHPs Case Williams and Noah Davis.
On Tuesday, Cincinnati acquired RHP Cessa and LHP Wilson from the Yankees for a player to be named.
The trio gives the second-place Reds relief help as they chase first-place Milwaukee in NL Central. Cincinnati entered Wednesday seven games behind the Brewers and was six games out of a wild-card spot.
The 31-year-old Givens, due to be a free agent after the season, has a 2.73 ERA and 27.4% strikeout rate in 29 2/3 innings for Colorado.
''We looked at all three as potential upgrades to our bullpen right now that can help us for the rest of the year,'' general manager Nick Krall said.
Reds: Krall hopes right-handed relievers Michael Feliz, Lucas Sims and Tejay Antone will return within the next month. Krall expects Feliz (right elbow sprain) back in a week to 10 days, and Sims (right elbow sprain) in about two weeks.
Cubs: SS Javier Baez (bruised heel) was held out of the lineup for a third straight day, but was available off the bench. . Hoerner, who started at shortstop, left in the eighth with an oblique strain. Bryant then moved from left field and filled in at shortstop for only the second time in his career. ... RHP Jake Arrieta (right hamstring tightness) will throw a bullpen Thursday. The Cubs placed the 2015 NL Cy Young Award winner on the 10-day injured list July 7 after he went 0-5 with a 9.67 ERA in eight starts following a win at Pittsburgh on May 25.
Reds RHP Luis Castillo (4-10, 4.12 ERA) faces Cubs RHP Alec Mills (4-3, 4.55) in the series finale Thursday afternoon. Castillo is 3-2 with a 1.71 ERA in his last 10 starts after going 1-8 with a 7.22 ERA in his first 11 outings this season.
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