Just because more than 100 games are remaining doesn't mean the St. Louis Cardinals are taking lightly a series against the rival they're chasing in the NL Central.

They haven't been playing all that well lately, but neither are the Chicago Cubs, who head to Busch Stadium for Monday night's opener in their worst slump of the season.

St. Louis (23-21) already trails the Cubs (29-13) by seven games and is just 12-13 at home. That includes Chicago taking two of three from April 18-20 in their first matchups this year.

"It is a series in May, but it's also an important series because it's against our division rivals," utility man Brandon Moss told MLB's official website. "It's a good opportunity for us to come out and play well and hopefully make up a couple games on them."

The Cubs are in town for three and will send former Cardinal John Lackey (4-2, 3.31 ERA) to the hill Monday before Jason Hammel and Jake Arrieta start the others.

Lackey made his return to Busch in the opener of the previous series and gave up four hits while striking out 11 in seven innings of a 5-0 victory. The right-hander has a 1.86 ERA over his last four outings after giving up one run in six innings of the Cubs' 2-1 victory over Milwaukee in 13 on Wednesday.

This time around against the Cardinals he'll oppose Adam Wainwright, who hasn't allowed a run in 20 innings over his last three starts against the Cubs.

Wainwright (4-3, 5.92) has had his struggles this season, but he's coming off his best outing after giving up six hits in 6 2/3 innings of Wednesday's 2-0 win over Colorado.

"It's very hard not to know kind of where you're at because people will tell you," Wainwright said. "Somebody will text you you're whole stat line. I know I've got probably 20-something more starts and a lot of really, really good things can happen."

Each of the right-hander's last three starts against the Cubs have come at Wrigley Field, and St. Louis is coming off dropping two of three to Arizona at home after losing 7-2 on Sunday.

Chicago is having its problems, too, while dropping five of its last seven. The Cubs are second in the NL in runs behind the Cardinals but are averaging 2.7 during their cold stretch.

They fell 1-0 at San Francisco on Sunday and have dropped two of three in back-to-back series. Chicago's first three hitters - Dexter Fowler, Anthony Rizzo and Kris Bryant - combined to go 0 for 10 as the club finished with a season low-tying three hits.

Former Cardinal Jason Heyward has sat out the last two after suffering a contusion on the right side of his ribs while making a diving catch Friday. He could miss at least part of this series while he recovers.

This is the first time since 2008 that the Cubs will enter in first place in two straight series against the Cardinals.

"There seems to be an extra little edge buzzing through the stadium when the Cubs come into town," manager Mike Matheny said. "It will be fun playing them."