With the Twins leading 4-1 in the fourth, Josh Willingham provided a two-run single, and the next batter, Morneau, deposited a pitch over the right-field fence with two men aboard to break the game open.
Walters (2-1) notched his first career complete game, yielding two runs on five hits in a 109-pitch performance. The right-hander walked two and struck out eight.
Chicago starter Gavin Floyd (3-5) was rocked for nine runs on eight hits, lasting only 3 2/3 innings.
Paul Konerko went 2-for-4 with an RBI for Chicago.