Lester went 7 1/3, surrendering four hits and striking out 10. His only hiccup was against Arenado in the fourth inning, when the Rockies third baseman hit a first-pitch fastball into the left-field basket.
Arenado came back with another homer in the ninth against Justin Grimm, Arenado's sixth of the season.
Miguel Castro and Jake McGee finished Chatwood's work in the eighth and ninth as the Rockies won for the fourth time in five games. Colorado improved to 7-5, and the Cubs moved to 9-3.
MOMENTS THAT MATTERED
Taking his shot: A day after going 0-for-4 on his 25th birthday against Jake Arrieta, Arenado entered Sunday 1-for-9 in the previous two games -- the only hit being a rare (for him) bunt single.