Jake Arrieta said he didn't feel sharp and that he was a little bit off Tuesday night.
The NL Cy Young Award candidate still tossed a three-hitter.
Arrieta became the first pitcher in the major leagues to reach 20 victories, Kris Bryant set the Cubs rookie record for home runs and Chicago inched closer to a playoff berth with a 4-0 win over the Milwaukee Brewers.
Looking loose after manager Joe Maddon entertained the team with a petting zoo in the outfield at Wrigley Field before the game, Arrieta (20-6) struck out 11 for Chicago, whose magic number for making its first postseason in seven years dropped to three.
The right-hander retired 14 in a row in one stretch in becoming the first Cubs pitcher to win 20 games since Jon Lieber in 2001.
"I've alluded to it before but it just means that I'm putting my team in positions to win ballgames," Arrieta said. "At the end of the day that's our goal, is to try and pile on as many as we can especially with where we're at in the season."
Bryant, whose April 17 debut was one of the most anticipated in years, hit a two-run homer in the third off Tyler Cravy (0-8) to give Chicago a 2-0 lead. It was Bryant's 26th longball, besting Billy Williams' mark in 1961. Bryant added a run-scoring double in the eighth.
He also relished a curtain-call after his third-inning drive.
"That was a special moment for me to get up on the steps and get that recognition," Bryant said. "It was something I'll never forget."
Kyle Schwarber was credited with an RBI double in the fifth when shortstop Jean Segura couldn't catch his high popup to short right field, allowing Dexter Fowler to score.
But Tuesday belonged to Arrieta, who added another accomplishment to a fine season that included a no-hitter Aug. 30 at the Los Angeles Dodgers.
"Jake is good," Maddon deadpanned as he began his postgame news conference. "That was outstanding once again."
By beating Milwaukee, Arrieta became the first Chicago pitcher since Hall of Famer Fergie Jenkins in 1971 to win at least 20 games and strike out at least 200 in a season. He also lowered his ERA to 1.88, giving him a chance to become the Cubs' first qualifying starter with a sub-2.00 ERA since Grover Cleveland Alexander had a 1.91 mark in 1920.
"He's got four good pitches." Brewers manager Craig Counsell said of Arrieta. "How many guys have four good pitches?"
Arrieta also lowered his ERA to 0.86 since the All-Star break, which would be a major league record, and he continued perhaps his best stretch of the season.
"It's hard to say otherwise," Arrieta said. "It's been good. It's been consistent."
Cravy went four innings and allowed two runs and three hits for the Brewers, who lost their 10th in 11.
"At this point in the season, he's pretty much going to capitalize on a miss every time," Cravy said. "(Bryant) got me tonight."