The Brewers, sitting in last place in the NL Central, won for the third time in eight games and ended the Cubs' winning streak at three. Reliever Brandon Kintzler (3-0) pitched a scoreless eighth for the victory.
Cubs reliever Pedro Strop (1-1) gave up the single to Gomez on an 0-2 pitch and Jean Segura easily scored from second to give the Brewers a 1-0 lead. With one out and the bases loaded, Jeff Bianchi gave the Brewers insurance with a double to right to score two more runs and Rickie Weeks also added a two-run double as Milwaukee batted around in the ninth.
Lohse, signed in the offseason as a free agent, pitched around five hits and three walks with six strikeouts. He has allowed only one run in his past 19 innings.
"He's done what we hoped he would do. He's done his job, we haven't supported him that much. It's too bad because the record with the way he's pitched should be better," said Brewers manager Ron Roenicke.
The normally soft-spoken veteran took a leadership role during a team meeting Friday.
"We got a lot of guys with opportunities right now. We have to take a hold of those opportunities and show people what we can do. We got a lot of young guys, just because the season is going the way it has doesn't mean we just show up and go through the motions," said Lohse.
On a cool July night, the Cubs opened an eight-game homestand with a somewhat different look. Left fielder Alfonso Soriano and pitcher Matt Garza were both traded while the Cubs were on a 10-game road trip as team president Theo Epstein continues the rebuilding process.
In his Wrigley Field debut, left fielder Junior Lake was 2-for-4, breaking out of an 0-for-14 slump.
Chicago's Jeff Samardzija also didn't factor in the decision despite a strong outing, pitching seven innings and allowing just three hits with two walks and seven strikeouts.
"I was pretty happy with how everything went. I kept the walks down. The leadoff hitter I got out a lot. Pretty efficient out there," said Samardzija. "I really feel like I'm improving as a pitcher, which feels really good to go out there and make some pitches in the game where you made the right choice and you get the right result."
With runners on first and second with one out in the sixth, Samardzija knocked down Norichika Aoki's comebacker with his bare hand to retire him at first. After being checked out by a team trainer and a few practice pitches to see if he could continue, Samardzija struck out Segura looking to end the inning.
Samardzija was 1-2 with a 6.85 ERA in his four previous July starts. Samardzija's name has sporadically come up during trade rumors, but the right-hander is not concerned.
"No. Not at all. It wouldn't be a good move. I haven't thought about it at all. I like where I'm at right now to tell you the truth," Samardzija said.
Before the game, the Cubs observed a moment of silence for former pitcher Frank Castillo. Castillo apparently drowned at a lake northeast of Phoenix on Sunday. Castillo had an 82-104 record in 13 major league seasons. He pitched for the Cubs, Colorado, Detroit, Toronto, Boston and Florida from 1991 to 2005 before retiring and lived in the Phoenix suburb of Scottsdale. He was 44. He was with the Cubs from 1991 to 1997. ... The Cubs and the Brewers are scheduled for a day-night doubleheader Tuesday. ... Segura was back in the lineup after missing Sunday's game with forearm tightness.