After scoring 25 points in the opener Butler put up 31 in game two, 14 of which came in the fourth quarter as he registered a personal post-season high.
The Bucks were in the hunt to level the series, but Butler hit four of five in the fourth and all three three-pointers.
Derrick Rose scored all 15 of his points in the second half, while Pau Gasol added 11 points, 16 rebounds and four blocks. Joakim Noah grabbed 19 rebounds.
Khris Middleton led the sixth-seeded Bucks with 22 points while Michael Carter-Williams scored 12.
Game three is Thursday at Milwaukee.