Lohse (5-1) allowed three runs on seven hits -- all before the fourth inning -- in seven frames to help the Brewers snap a brief two-game road losing skid and move to 13-5 away from home this season.
Jean Segura went 3-for-5 with two RBI for Milwaukee and Jonathan Lucroy also drive in a run in the triumph.
Darwin Barney and Junior Lake each homered for the slumping Cubs, who have dropped 10 of their last 12 following a three-game winning streak from April 30-May 3.
Chicago ace Jeff Samardzija's winless streak moved to 15 games going back to last season after yet another disappointing setback. The right-hander entered Friday's matchup with the second-best ERA (1.45) in the majors, but was the first pitcher since at least 1900 to give up three or fewer runs in his first eight starts of a season without earning a win. His last victory came on Aug. 24 of last season
Samardzija (0-4) surrendered all four runs -- two earned -- on six hits with six strikeouts over five innings.
The Brewers quickly got to work against Samardzija, manufacturing a pair of runs in both the first and second innings.
Segura singled with one out in the first and moved to second on a wild pitch. Lucroy then looped a single to left, which Lake fumbled to allow him to take second as the speedy Segura trotted home easily on the play.
Elian Herrera doubled to start the second and Logan Schafer walked before both runners advanced on a passed ball by Cubs catcher Welington Castillo. Segura then doubled the spread, plating both runners with a line-drive single back up the middle.
Barney's two-run shot in the home half barely cleared the wall in left but cut the Cubs' deficit in half, and Lake's third-inning solo blast made it 4-3.
Will Smith took over for Lohse and needed just 11 pitches to get through the eighth inning, and Francisco Rodriguez pitched around Castro's leadoff single in the ninth to record his 17th save of the season in as many tries.