Ian Desmond hit a 486-foot homer, longest in the Majors this season, and Nolan Arenado and Charlie Blackmon also went deep for the Rockies, who trailed 4-0 early but still won their ninth straight at home. Anthony Rizzo, Kyle Schwarber and David Bote homered for the Cubs.
Steve Cishek (1-3) gave up two hits in the ninth.
The teams used the long ball to put up four runs each in the third inning. Bote and Schwarber went back-to-back on consecutive pitches to score the first two, and Rizzo hit a two-run homer to center to give Chicago a 4-0 lead. Rizzo finished with three hits.
Blackmon and Arenado each had a two-run homer off Yu Darvish in the bottom of the inning to tie it. Desmond gave the Rockies a 5-4 lead with his mammoth pinch-hit homer in the seventh, but the Cubs tied it in the eighth on Javier Baez's groundout off Scott Oberg (4-0).
Darvish and Rockies starter German Marquez each allowed four runs in six innings.
Cubs: 3B Kris Bryant rolled his ankle against St. Louis on Sunday but was in the lineup.
Rockies: Colorado placed RHP Seunghwan Oh on the 10-day injured with a left abdominal strain, retroactive to Friday, and purchased the contract of LHP Phillip Diehl from Triple-A Albuquerque.
Chicago outfielder Carlos Gonzalez made his first appearance at Coors Field in a different uniform. Gonzalez played 10 seasons with the Rockies, becoming a free agent after last season. He signed with the Cubs on June 1 after hitting .210 in 30 games with Cleveland.
His return to Colorado was bittersweet for the three-time All-Star and 2010 NL batting champ.
"Obviously, this is home for me," he said before the game. "I got a lot of memories of this place. It is what it is. I'm now on the other side."
Gonzalez, who was 0 for 3 with a walk Monday, made his Cubs debut against the Rockies in Chicago last week, two days after signing with the club.
"I was home waiting for a job and the next thing I know I'm playing couple of games in Triple-A and hours later playing against my ex-teammates," he said. "It was great seeing them competing against each other."
Colorado rookie right-hander Peter Lambert (1-0, 1.29 ERA) makes his Coors Field debut on Tuesday night, five days after winning his first major league start when he beat the Cubs. Chicago left-hander Jose Quintana (4-5, 3.77) took the loss in that game and is on the mound for his fourth career start at Colorado.