It seemed like everyone helped out.
Schwarber hit a three-run homer and made a diving catch in left field, and the Cubs beat the Cincinnati Reds 8-2 on Monday night for their fifth straight victory.
Castellanos added a two-run double in the eighth inning as Chicago moved a season-high 14 games above .500. The Cubs have outscored opponents 59-18 during their streak.
"This is the time,'' Castellanos said. "We're facing adversity, and we've got to stare it down. There's a lot of guys in this room who've got to step up.''
Castellanos became the third right-handed hitter in MLB history to record at least 55 doubles and 25 homers in a season, joining Hall of Famers Hank Greenberg (1934) and Joe Medwick (1937).
The Cubs (82-68) pulled within a half-game of Washington for the top spot in the wild-card standings and stayed two games back of National League Central-leading St. Louis, which held off the Nationals for a 4-2 win.
It was Mills' first major league win in his 17th big league appearance.
"Every time he shows up, he does something good for us,'' manager Joe Maddon said, "and he does it in a very quiet, professional manner. He's outstanding.''
Cincinnati (70-81) had won three of four, but the Reds went 1-for-9 with runners in scoring position and left 11 runners on base.
"We had opportunities early and didn't get enough out of those,'' manager David Bell said. "It turns out that was kind of the difference.''
Kevin Gausman (3-9) pitched two innings in his first start since the Reds claimed him off waivers from the Braves last month. The right-hander has been a starter for most of his career, and Bell wanted to give him another look in that spot while giving the rest of his rotation an extra day of rest.
Gausman got into trouble in the first when Chicago put runners on first and second with one out. Schwarber then connected for the second straight day, driving a 2-2 pitch deep to center.
"I kind of put my team in a hole right there,'' Gausman said.
It was No. 37 for Schwarber, the highest total for a lefty batter for the Cubs since Hall of Famer Billy Williams hit 37 in 1972.
Schwarber also robbed pinch hitter Derek Dietrich with a stellar grab on his liner to left in the fourth. Phillip Ervin's sacrifice fly cut Chicago's lead to 3-2, but Cishek struck out Eugenio Suarez looking to end the inning.
The Reds promoted infielder Christian Colon from Triple-A Louisville. Colon was hit by a pitch while batting for Gausman in the third and scored on Curt Casali's bases-loaded walk. It was Colon's first major league appearance since June 20, 2017, for Miami against Washington.
Reds: SS Jose Iglesias (sore back) was out of the starting lineup. Bell said Iglesias likely will start Tuesday. ... SS Freddy Galvis missed his second straight game with left knee soreness. Bell said Galvis doesn't have meniscus or ligament damage and won't be out long-term.
Cubs: RH reliever Brandon Kintzler is dealing with a mild left oblique strain. ... Closer Craig Kimbrel (right elbow inflammation) is scheduled to throw a simulated game Tuesday and could return this weekend. ... SS Addison Russell (concussion protocol) hit off a tee before the game.
RHP Sonny Gray (10-7, 2.80 ERA) faces RHP Yu Darvish (6-6, 3.97 ERA) on Tuesday night in a matchup of two of baseball's best pitchers since the All-Star break. Gray is 4-1 with a 1.29 ERA in his last eight starts for Cincinnati. Darvish struck out 14 while pitching six scoreless innings in Chicago's 4-1 victory at San Diego on Thursday.
The Associated Press contributed to this report.
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