CHICAGO -- Chicago Cubs manager Joe Maddon called up Kyle Schwarber on Friday night to let him know he was planning to bat the struggling outfielder ninth on Saturday afternoon against the St. Louis Cardinals.

Schwarber accepted the decision -- and then he did something about it. Schwarber hit his first career grand slam to put the Cubs ahead in a 5-3 victory over the Cardinals.

Schwarber homered on the first pitch after Mike Leake allowed two singles and hit a batter to load the bases in the seventh inning.

Entering the game with a .163 batting average, Schwarber was hitting at the bottom of the lineup after the Cubs tried him at seventh Friday.

"It's nice to come up in that spot and be able to help out," Schwarber said. "It's kind of a sigh of relief. I want to go up there and help my team. For me to do that was great."

Maddon said he moved Schwarber to the ninth spot because he disliked the results of Schwarber batting seventh on Friday, when he went 0-for-2 with two strikeouts. Schwarber struggled in the leadoff role earlier this season.

"I'm like,' hey, at least I'm playing,'" Schwarber joked about his reaction to Maddon telling him he'd bat ninth. "I didn't say anything. He told me his reason, and I was like, all right. I'm going with it.

"Whatever the skipper does, I'm going to follow it. We've got his back, he's got our back. It's all a process. It worked out today."

Schwarber credited the support of his team. His four RBIs tied a career high, and he leads the Cubs with six game-winning RBIs this season.

"That was a big swing for him personally, obviously for the team," starting pitcher Jon Lester said about Schwarber. "Hopefully, this is signs of good things to come. You've seen his at-bats probably the last four or five days. I feel like his at-bats have gotten good, he's seeing pitches. He's back to being Schwarbs."

Javier Baez also homered for the Cubs, who have won two straight after losing six in a row.

Wade Davis posted his 12th save and Hector Rondon (1-1) notched the win.

Leake (5-4), who was leading the National League with a 2.24 ERA, gave up all but one of his five runs in the seventh inning. He exited after issuing a walk following Schwarber's ninth home run of the season.

"He had a five-pitch inning the inning before," Cardinals manager Mike Matheny said about sticking with Leake to pitch against Schwarber. "He looked good. We made a decision to let him get that last out and it didn't work.

"The fact that he's been one of the best pitchers in the league, down a couple guys in the bullpen who can potentially come into that spot and felt Mike was going to give us our best chance."

"It was slightly elevated and slightly on the plate a little too much for him," Leake said about the pitch to Schwarber.

The Cubs rallied after Lester gave up three runs and six hits in six innings, raising his ERA to 3.91.

Lester was coming off a rough outing against the Los Angeles Dodgers, when he allowed a season-high six runs in 3 1/3 innings. Entering Saturday, Lester owned a 1.80 ERA at home compared with a 7.11 road ERA.

Yadier Molina extended the Cardinals' lead to 3-1 with his sixth home run, a full-count, two-out solo shot in the sixth inning. Lester has allowed three home runs in his last two starts.

The Cardinals went ahead on Jose Martinez's two-run single after Lester loaded the bases with no outs on a walk, a bunt single and another walk in the first inning.

"It was nice to get a couple in the first and put pressure on," Matheny said. "Second, we get in a good position to add on and keep momentum going in a positive direction and unfortunately weren't able to keep that going right."

Baez's ninth home run -- a solo shot -- cut the lead in half in the third.

Lester, known for his troubles throwing to first base, picked Tommy Pham off first in the fifth inning.

NOTES: Cubs manager Joe Maddon said he had LF Kyle Schwarber bat ninth Saturday because the Cardinals took advantage of the eighth hitter and the pitcher being behind him Friday. Batting ninth, Schwarber is similar to another leadoff batter and gives him possibly one fewer at-bat, Maddon said. ... SS Addison Russell was out of the Cubs' starting lineup, but he pinch hit. He's batting .211. ... The Cardinals went with a right-handed lineup against LHP Jon Lester. OF Magneuris Sierra, who was called up from Double-A Springfield on Friday, was on the bench. ... INF Matt Carpenter was out of the Cardinals' starting lineup. He's hitting .216.