Starlin Castro and Scott Moore each hit two home runs for the Cubs.
Castro's second two-run shot — which barely cleared the center-field fence near the 433-foot sign at Cashman Field — gave the Cubs a 6-5 lead.
The Cubs added two runs and took an 8-5 lead in the seventh on Tyler Colvin's RBI single and Luis Montanez's sacrifice fly.
The Reds scored twice and trimmed the Cubs' lead to 8-7 in the seventh on Danny Dorn's solo homer and Chris McMurray's RBI single.
Scott Carroll was the winning pitcher while Robert Coello took the loss for the Cubs.