Lohse allowed three runs and seven hits as NL Central-leading Milwaukee won for the fifth time in six games. He retired his last 13 batters in his first win since April 23 against San Diego, ending a streak of three starts without a decision.
Jean Segura had three hits and two RBIs for Milwaukee, which improved to 15-9 against its division this year. Elian Herrera doubled twice in a spot start in right field for Ryan Braun, who got the day off as he makes his way back from a right oblique strain.
Darwin Barney hit a two-run homer and Junior Lake had a solo shot for the Cubs, who have lost three straight and 10 of 12. Jeff Samardzija lasted five innings after getting off to a slow start, but is winless in his last 15 games dating to last season.
Milwaukee jumped on Samardzija for two runs in each of the first two innings, taking advantage of several miscues by the Cubs on a soggy, cold day at Wrigley Field.
Segura singled with one out in the first, moved up on a wild pitch and scored on Jonathan Lucroy's base hit. Lucroy advanced when Lake mishandled his single to left and scored when Lyle Overbay reached on shortstop Starlin Castro's throwing error.
It was Castro's second error in three games and No. 7 in 40 games this season. The 24-year-old Castro had a career-low 22 errors in 159 games last season.
Segura added a two-run single in the second as Milwaukee opened a 4-0 lead. Welington Castillo had a costly passed ball that allowed the runners to move up to second and third before Segura hit a liner into center field.
Samardzija (0-4) allowed two earned runs and six hits in his shortest start of the season. His ERA increased from 1.45 to 1.62.
Barney connected in the second and Lake went deep in the third, but that was it for Chicago against Lohse (5-1). The veteran right-hander struck out two and walked one while improving to 6-6 in 21 career starts against the Cubs.
Braun was activated from the 15-day disabled list on Tuesday and played in three straight games against Pittsburgh. Manager Ron Roenicke decided to rest the 2011 NL MVP for the series opener against the lowly Cubs.
Braun, who is batting .316 with six homers and 18 RBIs in 25 games, did not make a rehab start before he rejoined the team.
''It's never a good situation when you have a guy, especially with an oblique to not have that rehab assignment,'' Roenicke said. ''You're going on what the player tells you. If he comes out and feels it again, you're in trouble. So that's why we try to take it easy so we're really protecting ourselves throwing him right out there and something happens and he's right back on the DL again.''
NOTES: It rained for much of the morning in Chicago, and the gametime temperature was 38 degrees. ... Brewers RHP Matt Garza (2-3, 4.98 ERA) is scheduled to face RHP Edwin Jackson (2-3, 4.56 ERA) on Saturday. It will be Garza's first game at Wrigley Field since he was traded from the Cubs to the Rangers last July. ... Roenicke said he hopes Carlos Gomez will be able to play Saturday. The center fielder is nursing a sore back while serving a three-game suspension for his role in a benches-clearing brawl April 20 in Pittsburgh.
Jay Cohen can be reached at http://www.twitter.com/jcohenap