CHICAGO -- Jake Arrieta said he felt a little off yet still delivered excellence on Tuesday.
"Today I didn't feel sharp, I felt off," he said. "Those days where you have a handful of starts where it's a tossup, you're not sure the way it's going to go. But your mindset plays a big deal in what the outcome looks like."
"You try to be mentally tough and grind it out."
"That first inning they got the runner on third base, he gets out of that mini jam right there and he's just dominant the rest of the way," said Cubs manager Joe Maddon.
The victory was the second straight and seventh in eight games for the Cubs (89-62) while the Brewers (63-88) dropped their second in a row and 10th in 11 games.
The Wrigley Field crowd stood and roared approval as Arrieta worked a one-two-three ninth that included two strikeouts.
"It's special, the crowd here appreciates it," Arrieta said. "They were into it from the first pitch and that's what makes playing this game so much fun, it's playing in front of your home crowd in a city like Chicago."
Arrieta (20-6) got all the support he needed on third baseman Kris Bryant's third-inning two-run home run.
Arrieta, 29, is the Cubs' first 20-game winner since Jon Lieber went 20-6 in 2001 and 27th Cub since 1900 to reach that milestone in a season.
It was his fifth straight outing of eight or more innings, his fourth complete game of the season and third complete-game shutout.
One was a no-hitter on Aug. 30 at the Dodgers, a 2-0 victory that included 12 strikeouts and just one walk.
"You've got to give him credit," Brewers left fielder Kris Davis said. "He hits his spots and he's got electric stuff -- swing and miss stuff in the zone. You've just got to battle and just hope we string (hits) together, but he's tough."
The last Cubs pitcher younger than 30 to win 20 games was Greg Maddux in 1992.
Arrieta also contributed at the plate, lining a two-out single to center in the seventh.
Bryant went 2-for-3 with three RBIs, including an eighth-inning RBI double that brought in Schwarber to make it 4-0. Schwarber was 2-for-3 and scored twice.
Milwaukee threatened in the first with second baseman Scooter Gennett's leadoff double and eventual advancement to third.
But Arrieta got the next three batters out, including his first strikeout of the game on first baseman Adam Lind.
Bryant gave Arrieta a 2-0 lead in the third inning with a two-out homer to left for his 26th of the season.
Bryant's shot, which broke Billy Williams' rookie Cubs home-run record set in 1961, came on a first pitch with two out and drove in Schwarber.
"I was joking around with (Arrieta) after the game and I told him he always has to outdo me," Bryant said. "But it's so much fun to play behind Jake. He works quick, throws a lot of strikes and he's one of the best pitchers in baseball."
Right-hander Tyler Cravy, as expected, had a short outing as he stepped into the rotation for starter Jimmy Nelson, now on the 60-day disabled list. Cravy (0-8) worked four innings in his first start since Aug. 18. He allowed two runs on three hits, struck out three and walked a pair.
NOTES: The Brewers recalled INF Yadiel Rivera and RHP Tyler Wagner from Double-A Biloxi. The team also selected the contracts of Yhonathan Barrios, RHP Adrian Houser, RHP Jorge Lopez and OF Michael Reed from Biloxi. All but Wagner will make their major league debuts. ... The Shuckers lost the best-of-five Southern League championship series to Chattanooga (Twins) 3-2. ... Brewers RHP Michael Blazek (fractured right hand) was transferred from the 15-day to the 60-day disabled list and RHP Jimmy Nelson (head contusion) was placed on the 60-day DL. ... Brewers RHP Zach Davies (1-2, 6.00 ERA) faces Cubs RHP Kyle Hendricks (7-6, 4.22 ERA) in Wednesday's season series finale. ... While RHP Jake Arrieta is the runaway leader in Cubs victories, LHP Jon Lester is also in double-digit territory (10-11), and Jason Hamel and Dan Haren still have a chance to break through with nine wins apiece and as many as two starts still ahead. ... Chicago's bullpen had an efficient 1.67 ERA in the last seven games. ... Cubs pitchers also top the major leagues with 1,312 strikeouts, four ahead of Cleveland heading into Tuesday's games.