It took a little while for the Chicago Cubs to get going this season after ending 108 years of frustration by winning the World Series last fall.

Now, the Cubs are on the verge of completing the first step toward defending their long-awaited championship -- winning a division title.

Chicago takes a magic number of two for clinching the National League Central into the opener of a four-game series against the St. Louis Cardinals at Busch Stadium on Monday.

The Cubs (87-68) were 43-45 and 5 1/2 games behind the Milwaukee Brewers at the All-Star break. They are 44-23 since the break and have been in sole possession of first place since beating the Arizona Diamondbacks on Aug. 13.

Milwaukee (82-74) sits 5 1/2 games back, and St. Louis (81-74) is six games back. Because the Brewers are idle Monday, the earliest the Cubs can clinch is Tuesday.

Chicago might have been able to clinch Monday if it completed a four-game sweep at Milwaukee. Instead it won three of four, taking the first two games in extra innings before Jose Quintana struck out 10 during a three-hitter during a 5-0 win Sunday.

Ben Zobrist is among those looking forward to clinching in front of Chicago's biggest rivals.

"It will be nice to do it there, I'll just say that," Zobrist said. "We have to win the games. It's a big series.

"We intend to clinch there, and I think for a lot of guys who have been around here for a long time, it'll be very satisfying."

Since scoring three times and getting swept in a three-game series at home against Milwaukee, the Cubs are 10-2 in their past 12 games. Three of those wins occurred Sept. 15-17 at Wrigley Field against St. Louis.

St. Louis is on the verge of being eliminated from the division race but is still alive in the wild-card chase. The Cardinals are 2 1/2 games behind the Colorado Rockies (84-72) for the second NL wild card.

The Cardinals rebounded from getting swept by winning four consecutive games, but they were outscored 15-7 in losing the final two games of their three-game series at Pittsburgh over the weekend.

"We just have to keep playing until mathematically you're out of it," St. Louis outfielder Tommy Pham said. "That's how you have to look at it. It's a very tough situation. We need some luck."

The Cardinals also need some better hitting. Matt Carpenter homered Sunday, but the offense went 3-for-15 with runners in scoring position in the two losses to Pittsburgh.

Another area not helping St. Louis is its performance against the Cubs. The Cardinals are 4-11 in the season series, hitting .222 and pitching to a 4.11 ERA in those games.

"We've got to find a way to win, and we've got to play them better," Carpenter said. "We haven't had enough to beat them to this point."

Besides potentially clinching, the Cubs would like to see Jon Lester (11-8, 4.56 ERA) finish the regular season well. He is 3-1 this month but owns a 5.91 ERA in his past four starts heading into a Monday outing at St. Louis.

The left-hander last pitched Wednesday when he allowed seven runs and eight hits in 4 1/3 innings at Tampa Bay. Lester also owns a 5.11 ERA since the All-Star break while working around a brief DL stint.

Lester is 1-1 with a 3.28 ERA in four starts against St. Louis this season. For his career, he is 4-4 with a 2.36 ERA in 13 starts against St. Louis.

Luke Weaver (7-1, 2.05 ERA) opens the series for St. Louis. He is on a seven-game winning streak, the longest by any St. Louis rookie since Ted Wilks in 1944 and the longest by any Cardinal since Matt Morris in 2001.

Weaver kept the streak alive by allowing two runs on five hits in five innings during a 9-2 win at Cincinnati on Wednesday. He has struck out at least seven in seven straight starts.

"For a young guy, he doesn't make a lot of mistakes in the middle of the plate," Cardinals manager Mike Matheny said of Weaver. "He's making quality pitches. It is fun to watch."

Weaver is facing the Cubs for the first time this season and making his fourth appearance against a contending team this season. He lost to the Arizona Diamondbacks on July 27 but struck out 18 in 12 innings during a pair of starts against Milwaukee last month.

The right-hander's only start against the Cubs occurred Aug. 13, 2013, in Chicago when he allowed two runs and four hits in four innings during a no-decision.