David Bote drove in the game-winning run with a bases-loaded walk in the 10th inning, lifting Chicago to a 6-5 victory over the Cincinnati Reds.
Javier Baez had two hits and two RBIs for the Cubs, who have won their last nine games in comeback fashion. Albert Almora Jr. and Ian Happ also had two hits apiece, and Addison Russell drove in three runs.
The Cubs trailed 4-3 in the seventh. They scored four times in the eighth inning on Saturday for an 8-7 win.
Eugenio Suarez and Adam Duvall homered for the Reds, who had their five-series winning streak snapped.
Luke Farrell (3-3) worked a clean 10th inning for the win.
Willson Contreras led off the 10th with a walk against Jackson Stephens (2-2). Contreras then advanced on a wild pitch with Victor Caratini at the plate. After Caratini struck out, Happ was intentionally walked.
Russell then hit a weak roller to first base. Joey Votto fielded the ball cleanly and had an easy play, but tried to take the ball out of his glove before reaching the bag - to hold Contreras at third - and bobbled it. Russell was initially called out, but the call was overturned following a review, loading the bases with one out. Votto was given an error.
Bote worked the count to 3-2 and then took a high fastball for ball four.
Baez's two-run single in the seventh gave the Cubs a 5-4 lead. But Duvall led off the ninth with a drive to left off Brandon Morrow. It was Morrow's second blown save of the season.
RHP Kyle Hendricks (5-8, 4.27 ERA) takes the mound in the opener of a three-game series at San Francisco tonight.