MILWAUKEE _ Addison Russell stepped up in place of injured shortstop Javier Baez by hitting a home run in the fifth inning.
But the rest of the offense didn't pick up the slack, and the bullpen didn't provide enough scoreless innings after tender-armed Yu Darvish pitched five scoreless.
The Cubs missed Baez's defense, as Russell committed a throwing error to start the ninth inning and enable the Brewers to seize a 3-2 victory Saturday night at Miller Park.
Christian Yelich battled from an 0-2 count against Brandon Kintzler to slice a double past left fielder Kyle Schwarber with two outs to score Tyler Austin from first base with the winning run. Austin reached on Russell's error, which pulled first baseman Anthony Rizzo well off the base.
It added up to another frustrating loss that damaged the Cubs' chances of overtaking the Cardinals in the National League Central, as they fell 3 { games behind with 21 left.
And the Cubs' lead over the Diamondbacks for the second wild-card spot was reduced to 1 { games.
The Cubs missed a chance to score more than the tiebreaking run after loading the bases with no outs in the top of the eighth. After Rizzo drew a one-out walk off Josh Hader to put the Cubs ahead 2-1, Kris Bryant popped to third and David Bote struck out.
That haunted them immediately as Yasmani Grandal smacked David Phelps' first pitch _ a hanging breaking pitch _ for a tying home run. The Brewers loaded the bases with two outs before Rowan Wick induced Orlando Arcia to fly out to right.
With Baez possibly lost for the remainder of the regular season after an MRI revealed a hairline fracture of his left thumb, Russell will be leaned on more heavily to provide steady defense and more offense.
Russell was hitless in his previous 16 at-bats before hitting a home run that cleared the center-field fence and the outstretched glove of Trent Grisham to snap a scoreless tie in the fifth.
Prior to Russell's homer, the Cubs had only one hit: a single to right by Victor Caratini to lead off the third.
But left-hander Gio Gonzalez, who held the Cubs scoreless despite walking four in the first three innings of a 4-1 win on Sept. 1, induced Albert Almora Jr. to ground into a double play, and Bote grounded into a double play to end a rally in the fourth.
Darvish showed no lingering effects Saturday night from the right forearm tightness that forced him to miss his last start.
Relying on a knuckle curve and a fastball that topped out at 96 mph, Darvish limited the Brewers to three hits in five shutout innings.
Darvish, who has dealt with discomfort for the last two months, allowed only two runners to reach second base. He struck out Eric Thames with runners at first and second to end the first inning and retired three consecutive batters in the fourth after Yelich led off with a single and stole second.
Darvish allowed three hits and a walk while striking out seven in a 72-pitch stint.
The Cubs on Saturday also adjusted their rotation, moving left-hander Jon Lester to start Sunday's series finale and pushing Kyle Hendricks' start to Monday night against the Padres in San Diego.
Manager Joe Maddon said the switch was made to give the Cubs more favorable matchups. Lester is 5-3 with a 2.10 ERA in 10 career starts against the Brewers, while Hendricks is 5-2 with a 2.98 ERA in nine starts against the Padres.
Catcher Willson Contreras didn't start for the second consecutive game as a precautionary measure after missing a month because of a strained right hamstring. Contreras started Tuesday and Thursday but sat out Friday.
"You always want to play, but you've got to follow the plan and understand there's a lot of games to keep playing," Contreras said before the game.
