Baez was 0-for-5 with three strikeouts before driving a first-pitch fastball from Boone Logan (2-2) out to right-center field to lead off the 12th, making him the first player to homer in extra innings in his big-league debut since Miguel Cabrera in 2003. Welington Castillo also went deep and drove in two runs for the Cubs, who went to extra frames for the fourth time in their last seven games and improved to 6-8 in extra-inning contests this season.

Nolan Arenado collected three hits, including a game-tying blast in the seventh, and Brandon Barnes added two RBIs for the Rockies, who have dropped five straight. Charlie Culberson forged a 5-5 tie with an RBI single in the 11th after Ryan Sweeney's bloop base hit in the top of the inning had given the Cubs the lead.

Barnes doubled in a pair of runs in the second and Colorado made it 3-0 on Josh Rutledge's RBI single in the fifth. Castillo's eighth homer - matching his career high set last season - got the Cubs on the board in the sixth, and Chicago scored three runs without the benefit of a hit in the seventh, taking advantage of the Rockies' franchise record-tying six walks to take a 4-3 lead.

Arenado's 10th homer of the season in the bottom of the frame knotted the contest, and the Rockies led off the 10th with back-to-back singles and a sacrifice before Brian Schlitter got Barnes to ground into a double play. Baez's blast made a winner of Hector Rondon (3-3), who blew the lead in the 11th, and Carlos Villanueva worked a scoreless 12th for his second save.

GAME NOTEBOOK: Rockies LHP Brett Anderson left after three scoreless innings with lower-back spasms and is day-to-day. … Cubs LHP Travis Wood allowed three runs and seven hits over six innings, remaining winless in nine starts since June 15. … Chicago 1B Anthony Rizzo went 0-for-5 to snap his eight-game hitting streak.