Carlos Gomez hit his first career grand slam and tied his career high with five RBIs, leading Milwaukee over Cincinnati 12-1 Friday night and extending the Brewers' winning streak to six.
Lorenzen (3-3) threw 90 pitches while giving up three runs and five hits in four innings.
"That's a really good team," Lorenzen said. "They had a couple of good series coming in. I could have done better with my pitch selection. You second-guess yourself sometimes. When you don't throw with conviction, this happens. You learn from it."
Gerardo Parra and Aramis Ramirez added solo shots for the Brewers, on their longest winning streak since taking nine in a row in April 2014. Gomez, Jonathan Lucroy and Ryan Braun had three hits each as Milwaukee matched its season high for runs and victory margin.
"We know we can hit," Gomez said. "It just seems like, this whole year, we were never able to put it together. When we get five or six guys extremely hot, we know we can make some runs."
Mike Fiers (4-7) allowed three hits in seven scoreless innings to win for the first time in four starts since June 12. He didn't allow a runner past first base until Marlon Byrd reached second on Fiers' throwing error in the seventh.
"We're locked in right now," said Fiers, who did not get a decision in his previous two starts while allowing three runs in 13 innings. "This is what we envisioned the whole season."
Gomez homered into the left-field seats in the seventh against Carlos Contreras, Gomez's sixth homer this season and first since May 29.
"He started out 0 for 2, then he hits three line drives," Brewers' manager Craig Counsell said.
Milwaukee, which totaled 28 runs while sweeping a four-game series at Philadelphia, sent the Reds to their largest margin of defeat this season.
Fans in the sellout crowd of 40,760 had barely settled in when Parra opened the game with his sixth homer of the season and seventh leadoff homer of his career, including two this season. Milwaukee's first three batters had hits, and Lucroy scored on Adam Lind's groundout for a 2-0 lead.
Ramirez hit Lorenzen's first pitch of the second inning for his 10th homer of the season.
"Michael got a lot of his hard stuff up against a hot-hitting team," Reds manager Bryan Price said. "They got his pitch count up and took advantage of our bullpen."
Reds 3B Todd Frazier looked Ryan Braun back on a routine first-inning grounder, turned to throw to first as Braun took a couple of steps toward the plate, then whirled and made a diving tag as Braun lunged for the bag. The original safe call was overturned and Braun was out, helping the Reds limit Milwaukee to two runs in the inning.
HOLE IN THE LINEUP
While every other Brewers starting position player had least one hit, Adam Lind went 0 for 4. He entered with an 11-game hitting streak, Milwaukee' longest this season.
Brewers: What Counsell described as an overworked bullpen prompted Milwaukee to recall rookie RHP Tyler Cravy and David Goforth from Triple-A Colorado Springs. Rookie RHP Corey Knebel and IF/OF Jason Rogers were optioned to the Sky Sox, leaving Counsell with an eight-man bullpen.
Reds: LHP Tony Cingrani (shoulder) turned in two hitless, shutout innings for Triple-A Louisville in the first appearance of his rehab assignment on Friday. He allowed one walk with three strikeouts while throwing 23 of 35 pitches for strikes.
Brewers: RHP Jimmy Nelson (5-8) is 0-1 with a 6.97 ERA in two starts against Cincinnati this year.
Reds: RHP Josh Smith (0-1, 5.63) makes his first career start at Great American Ball Park on Saturday. Smith was promoted from Triple-A Louisville on June 23 and made two starts on the Reds' last trip.