Kyle Lohse (1-1) went five innings, allowing one run and five hits, but left in the sixth after dislocating his left pinkie when he caught the finger on the elbow of Padres second baseman Jedd Gyorko, who was covering first, after an unsuccessful sacrifice bunt. Lohse struck out four and walked one.
The right-hander thinks he'll be able to make his next scheduled start.
Marquis (1-2) was rocked for seven runs in four-plus innings as the Padres dropped their fourth in a row overall and sixth straight at home.
The homer for Braun was his sixth of the season. He also had an RBI single in the fifth and has 19 RBIs.
In his last visit to Petco Park, Braun became the first player to hit three home runs in one game at the ballpark. He also had a triple in his last at-bat here on April 30, 2012. He has five homers and 13 RBIs in 16 games at Petco.
Betancourt's home run, his third, came after Marquis had hit consecutive batters—Logan Schafer and Carlos Gomez—with two outs.
The Brewers have hit 15 home runs in eight games after hitting five homers in their first 10.
Milwaukee had scored just five runs in Lohse's first three starts before putting up a five-spot in the first inning on Monday.
The Brewers added two more runs in the fifth, one on Braun's RBI single and they scored on a wild pitch by Padres reliever Anthony Bass with the bases loaded.
The Padres, who were shutout in San Francisco Saturday and Sunday, snapped their 25-inning scoreless streak with a run in the fifth on a double by Gyorko and an RBI fielder's choice by Bass.
NOTES: Padres OF Carlos Quentin, who served the last game of his eight-game suspension Monday for his part in the benches-clearing brawl in which Dodgers star Zack Greinke broke his collarbone, will be back in the Padres lineup Tuesday. . Padres 1B Kyle Blanks wasn't in the starting lineup, but was available for pinch-hitting duty Monday night, a day after sustaining a cut on his left eyelid when he was cut by his sunglasses as he smacked into the left field wall making a catch in the sixth inning at San Francisco. "I feel definitely better than yesterday," said Blanks. "It's going to be a kind of a touch and feel progression. I saw it (on replay) and it reminded me of how fun it wasn't, but my head feels good, neck feels fine, mainly it's just a lot of soreness in my shoulder." Padres' manager Bud Black said that Blanks had stitches in his eyelid just below his eyebrow. ... Black also said that LHP Clayton Richard (0-1, 5.28) was feeling better after a stomach flu cancelled his start in San Francisco and that he would be on the mound Tuesday against Milwaukee's Yovani Gallardo (1-1, 5.24). ... Brewers manager Ron Roenicke said that RF Norichika Aoki, who has appeared in all 17 games for Milwaukee, would get Monday night off but would be back in the starting lineup Tuesday. ... Roenicke also said that he has not yet decided whether rookie RHP Hiram Burgos, who won his major league debut against the Cubs, would remain in the Brewers rotation. "It all depends on matchups. We don't mind sliding him back in again then pushing the other guys to six days, but we're going to look at matchups."