MILWAUKEE -- Dodgers starter Tony Gonsolin fired a first-pitch slider to Brewers rookie Joey Wiemer, who took a big hack and swung through the 88 mph offering on the outside corner.

When Gonsolin came back two pitches later with an 88 mph splitter on the inner half of the plate, Wiemer was all over it -- crushing a three-run homer that traveled a Statcast-projected 403 feet with a 108.8 mph exit velocity.

That one mistake in the fifth inning on Monday night spoiled an otherwise strong outing from Gonsolin in the Dodgers’ 9-3 series-opening loss at American Family Field.

“Tony threw the crap out of the baseball,” manager Dave Roberts said. “It was one mistake. I thought all of the stuff was really good.”

Gonsolin was looking to throw the pitch to Wiemer lower in the zone than where he left it: thigh-high in the middle-in part of the strike zone. Wiemer capitalized on the mistake, but Gonsolin was also victim of some tough luck leading up to it, as evidenced by his final line.

In six innings, Gonsolin was charged with three runs -- all unearned.

Brewers catcher William Contreras led off the fifth with a ground ball between third baseman Michael Busch and shortstop Miguel Rojas. Busch crossed in front of Rojas, bobbled the chance and picked it up with his bare hand. His throw to first base sailed wide of Freddie Freeman up the foul line.

“It's a play that he expects to make and could have been a different inning right there,” Roberts said of Busch, who professionally has 104 career innings at third. “But he's working hard over there at third base, and I wanted to get him in there. Unfortunately, we just didn't come up with that play right there.

“We’ve got to make plays,” Roberts added of his defense overall. “I think that if you're just giving teams extra outs, at some point in time, it's going to cost you -- and it does, regardless, as far as pitches, who we use, extending innings. Today it cost us. Guys are working hard, but you still got to go out there and make plays.”

Gonsolin struck out the next hitter in Brian Anderson and then got Brice Turang to ground into a fielder’s choice and a near-inning-ending double play. The frame continued on a ground-ball single up the middle by Tyrone Taylor, one that was just out of second baseman Mookie Betts’ reach.

Wiemer then came up and went deep.

Gonsolin bounced back with a 1-2-3 sixth inning. It wrapped up his best start since returning from a left ankle sprain, which landed him on the injured list for the first month of the season. Monday was his longest outing, as he went 3 1/3 and 4 2/3 innings in his first two starts. His six strikeouts and 11 whiffs against Milwaukee were season highs.

“I thought it was his best outing yet,” Roberts said. “Velocity, his secondary pitches, how he sequenced. Obviously left that pitch up to Wiemer. But that inning just kind of unfolded in a way that a couple balls had eyes.

“Tony threw the baseball well. First time he got through the sixth inning and I didn't want to push him anymore. Unfortunately, we couldn't keep those guys at bay tonight.”

“I felt like I was throwing a lot of strikes,” Gonsolin said. “I felt like I was able to manage the pitch count pretty well. Got deep into the game. Made one really bad pitch and it cost us the game.”

Granted, the Dodgers’ offense only had one run on the board before Chris Taylor’s pinch-hit two-run homer in the ninth inning. And Milwaukee also scored six runs against Los Angeles’ bullpen in the seventh to break things open.

The Dodgers were coming off an intense series against the Padres over the weekend, their first meeting this season since squaring off in the National League Division Series last fall. The finale on Sunday night went 10 innings, and Los Angeles got to Milwaukee early Monday morning.

Asked whether a performance like this one could have been predictable, considering those circumstances, Roberts instead credited the job done by Brewers starter Freddy Peralta. The right-hander yielded just one run on three hits and two walks in six innings.

“I thought the hangover was Peralta tonight,” Roberts said. “I thought we had some momentum coming into this series and felt good about it. But when you’ve got to face that guy, that sort of puts the momentum back in check.

“He was really good today. He was good and they got a timely hit.”