CHICAGO -- Three pitches into Monday night’s game at Wrigley Field, the boos that always greet Brewers outfielder Christian Yelich transformed into a collective gasp. Yelich jumped on a fastball from Cubs righty Jameson Taillon, sending it out to left-center for a leadoff home run.

This was not how the North Siders hoped to begin this crucial series.

“It happened kind of quick there early,” Taillon said.

The Brewers used a four-run first inning to send the Cubs to a 6-2 loss in the opener of a three-game set between the I-94 rivals, who both have a division crown on their mind. Milwaukee has been one of the Majors’ hottest teams -- evidenced by its nine-game winning streak -- and Chicago has piled up wins in the second half to climb back into the playoff race.

Monday’s game was the first of 14 in a row for the Cubs against the National League Central-leading Brewers and the Wild Card-contending Reds, Giants and D-backs. The defeat knocked Chicago (69-62) five games behind Milwaukee (74-57) in the division, though the team still holds the second Wild Card position by a half-game over Arizona (69-63). With head-to-head record serving as the first tiebreaker in the standings, the Cubs fell to 3-5 in the season series against the Brewers with five matchups remaining.

Every game, series and week carries increased magnitude at the moment.

“That’s this time of year for everybody, right?” Cubs left fielder Ian Happ said. “You have a month left to play really good baseball and put yourself in a position to be playing in October. No matter who you’re playing, that’s the case.

“We’re just going to take it one game at a time. You can’t think too far ahead. We’ve got the right group and the right people in place to have that mentality.”

Coming off a 5-2 road trip against the Tigers and the Pirates, the Cubs were in an opportunistic position with the Brewers coming to the Friendly Confines. Any hope of leaning into that perceived momentum went by the wayside when Yelich ignited Milwaukee’s early strike.

After Yelich’s leadoff blast, Taillon allowed a one-out single to Sal Frelick. Willy Adames then pulled a chopper into the hole, where shortstop Dansby Swanson ran it down but then made an errant throw to second. The misplay allowed both runners to move up 90 feet, setting up a sacrifice fly (Rowdy Tellez) and a two-run homer (Mark Canha) that promptly put Taillon and the Cubs up against a wall.

“The ball that Adames hit me -- that play should get made pretty much 100 out of 100 times,” Swanson said. “It didn’t, and they obviously took advantage of it. They were really opportunistic tonight. You’ve got to give them a little bit of credit for taking advantage of our mistakes.”

The four runs by the Brewers gave the Cubs 31 first-inning runs allowed in the second half, the most in the NL in that stretch. Taillon noted that both homers came via fastballs in 2-0 counts, adding that, no matter what happened behind him, he needed to execute better in those moments.

Cubs manager David Ross echoed that sentiment.

“There were a couple plays we could have made behind him that would’ve limited the damage a little bit,” Ross said. “But it looked like just [his execution was off]. There was a lot of hard contact early on. It was loud. They weren’t missing mistakes.”

Taillon did find a rhythm as the game wore on, though, giving the Cubs six innings to help ease the burden on a taxed bullpen.

“I just did a better job of -- whether it was getting ahead and attacking or just when I’m behind in the count -- being a little more aware,” Taillon said. “They know I’m a strike thrower, so if I’m 2-0, they know I want to get back in the count, and they were just jumping heaters.”

That early lead allowed veteran Brewers lefty Wade Miley to work quickly and pump the zone with strikes against his former team. Miley yielded solo homers to Happ and Patrick Wisdom but little else in dispatching the Cubs. Milwaukee’s stingy bullpen finished the job from there.

“To start out a road series and a game that everybody’s anticipating a good atmosphere from the crowd, doing that to the home team in the first inning -- what more can you ask, really?” Brewers manager Craig Counsell said. “You couldn’t start a game out better.”

Well, the Cubs would disagree with that particular assessment.

“The biggest thing for us is just playing our brand of baseball,” Swanson said. “Obviously, we didn’t do that tonight, but I know that we’re capable of so much more, and we’ll be able to come out tomorrow and play better.”