CHICAGO -- The Chicago Cubs own a staggering 13-game lead over the St. Louis Cardinals in the National League Central.

But manager Joe Maddon is keeping focused and calm.

The teams wrap up a four-game series Sunday night at Wrigley Field.

The Cubs (73-42) took the first two games before the Cardinals won 8-4 on Saturday to snap Chicago's 11-game winning streak.

"My thought process hasn't changed at all," Maddon said about handling the big lead. "It's when you get ready and you walk out there, where's your mind? It's all about your mind. If your mind is locked in and if you're really, truly focused on today, it's pretty easy.

"If you want to take the blinders off and open this whole thing up and look at the macro component, you might get somewhat complacent or lazy, or your focus may wonder. As long as you just approach today, it doesn't matter."

Right-hander John Lackey (9-7, 3.56 ERA) will take the mound for the Cubs and try for his fifth straight quality start. He allowed three hits and one run in eight innings in a 5-1 victory over the Los Angeles Angels in his last start Tuesday.

The Cubs are getting used to his emotional side.

"He's not going to be out there smiling and he's going to be upset with the umpires," Maddon told MLB.com. "He's going to be upset with his manager. He's going to be upset with teammates on occasion, but that's who he is. When you know that, it's OK."

Lackey is 1-1 with a 2.70 ERA this season in three starts against the Cardinals -- his only starts against his former team. He went 16-13 with a 3.10 ERA in 43 starts with St. Louis from 2014-15.

The Cubs are 6-6 against St. Louis this season.

For the Cardinals, right-hander Mike Leake (8-9, 4.79) is expected to start. In his last outing, he walked a season-high four, struck out none for the first time this season, and allowed three runs in six innings against his former team the Cincinnati Reds. He gave up 19 earned runs in his previous three starts.

Leake is 9-3 with a 3.18 ERA in 20 career starts against the Cubs. He ranks second among National League pitchers, behind Clayton Kershaw of the Los Angeles Dodgers, with a ratio of 1.42 walks per nine innings.

Though well behind the Cubs in the division, the Cardinals (61-56) remain in the mix for a wild card spot.

The Cardinals are looking for a leadoff hitter now that Matt Carpenter is batting third in the absence of Matt Holliday, who sustained a broken thumb when he was hit by a Mike Montgomery pitch Thursday. Greg Garcia went 0-for-5 batting leadoff Saturday, when Holliday went on the disabled list. Carpenter was 2-for-5 with three strikeouts.

"The three spot is as much psychological as it is strategic," manager Mike Matheny said. "We also need somebody to step up to be that guy at the top of the order. We have a few guys who look like they can help us, kind of give

us freedom to be a little more creative with Carpenter."

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