"That ball was beyond properly struck," Cubs manager Joe Maddon said. "If the back wall's not there, that's somewhere over, shoot, I don't know, what's on the other side? The lake? That ball was kilt. It was K-I-L-T, kilt."
The third-place Brewers dropped 7½ games behind first-place St. Louis in the NL Central and five back of the Cubs for the second wild card. Chicago remained 2½ behind the Cardinals, who routed San Francisco 10-0.
"It's a big series. We're fighting for the division," Schwarber said. "Whenever you're in their environment, and you can take the first game, it's a positive step. Now we have to focus on tomorrow and take game two."
The Cubs loaded the bases with one out in the sixth on two singles and a walk against Matt Albers (5-5). Drew Pomeranz relieved and Anthony Rizzo lined a sacrifice fly to right field that put Chicago up 5-4.
Willson Contreras reached on a swinging bunt to reload the bases. Schwarber then sent the first pitch 442 feet to right-center for his 34th homer and second grand slam of the season. "It was an inning where we got some unfriendly bounces and then they got a huge hit," Brewers manager Craig Counsell said. "That was the inning. The play with (David) Bote, that changes the start of the inning and then the Contreras swinging bunt keeps it alive. Then Schwarber had a huge hit. I thought Drew made good pitches. He threw his fastball up at the top of the zone, probably out of the zone in a couple instances. Give them credit, they did a nice job."
Jose Quintana (13-8) allowed four runs on five hits, including two homers, in five innings to improve to 9-1 in his last 12 starts. Contreras finished a triple short of the cycle, driving in two runs on four hits. On his second double, he rounded second in the eighth inning before heading back to the bag instead of trying for a triple.
Ben Zobrist reached five times with three singles and two walks, scoring three times. Bote, recalled from the minors earlier in the day, made it 10-5 in the ninth with his 11th homer. Yasmani Grandal brought the Brewers even at 4 in the fifth a two-run homer, his 23rd, off Quintana.
Contreras tied it with his 21st homer to open the fourth off Chase Anderson Rizzo's two-run double put the Cubs in front 4-2 in the fifth. Hernan Perez put the Brewers up 2-1 in the second with a two-run homer, his sixth.
"I think as a team, we have to focus on playing one game at a time," Anderson said. "If you focus on one game, it will lead to the next game. It would be nice to win three games, but tomorrow is our main focus. We have to worry about that first."
KIMBREL TO INJURED LIST Cubs closer Craig Kimbrel was placed on the 10-day IL with elbow inflammation, retroactive to Monday. The right-hander has not pitched since allowing a three-run homer to Milwaukee slugger Christian Yelich on Sunday. Bote was recalled from Triple-A Iowa.
TRAINER'S ROOM Cubs: All-Star SS Javier Baez was scratched from the starting lineup with lingering soreness in his left thumb. Brewers: 3B Mike Moustakas, bothered by a bruised left hand, was not in the lineup and is day-to-day. "It's more than just a bone bruise or a bruise to some tissue," Counsell said. "There are some other things being affected. The tendons in his hand are being affected and it's just not healing as quickly as we'd like." ... C Manny Pina left after the fourth inning with head discomfort, the team announced.
UP NEXT Cubs: LHP Cole Hamels (7-5, 3.69 ERA) makes his fifth start this season against Milwaukee. In his last start, also vs. the Brewers, he took the loss despite giving up just two runs in six innings. Hamels is 1-3 with a 6.43 ERA in his last seven starts.
Brewers: RHP Zach Davies (8-7, 3.76) is 0-5 with a 7.76 ERA over his last six starts. In his most recent start Saturday against the Cubs, he did not allow a run in 4 2/3 innings but did not get a decision.
More AP MLB: https://apnews.com/MLB and https://twitter.com/AP_Sports