Joe Maddon doesn't want his Chicago Cubs to make too much of this four-game home series with the San Francisco Giants. He just wants them to enjoy playing meaningful baseball in August.

After taking the opener, the Cubs try to increase their advantage over the Giants for the NL's second wild-card spot Friday.

Rookie Kyle Schwarber hit a three-run homer for his first at Wrigley Field as Chicago (59-48) moved one-half game ahead of San Francisco for that final wild-card position with Thursday's 5-4 victory. While this has the potential to be a season-defining series for the overachieving Cubs, their manager wants to keep things in perspective.

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"Whenever you're playing that game, you should not be nervous, upset, concerned or having to turn a dial up or turn a dial down because you're used to playing that game," Maddon told MLB's official website. "Just play for today."

Winners in seven of the last eight, the Cubs certainly understand the potential importance of the set but have followed their manager's lead.

"It's a huge series for us, but we're having fun with it," said Schwarber, 6 for 14 with half of his six home runs plus six RBIs in four games this month.

The Giants (59-49) are 4-5 since a 12-1 stretch and now face Jon Lester (6-8, 3.26 ERA), who is back on the mound after rain halted his start after 31 pitches during Monday's postponement at Pittsburgh.

''They're a talented club,'' San Francisco manager Bruce Bochy said. ''They're not going anywhere. That's a good club.''

Lester has a 1.66 ERA while going 2-2 and lasting at least seven innings in each of his last six starts. He set season highs of eight innings and 14 strikeouts while giving up two runs in a 3-2 victory over Colorado in his last official outing July 29.

''You got to figure out a way to go as deep as you can,'' Lester said.

He's allowed one run over 17 1-3 innings to win both starts against the Giants, but last faced them in 2013.

Mike Leake was scheduled to make his second start since being acquired by San Francisco last Thursday, but was scratched due to a mild hamstring strain.

"He thought it was a cramp, but it didn't go away," Bochy said.

Instead, Ryan Vogelsong (7-7, 4.16) makes his first start since yielding four runs, two homers and walking three in 5 2-3 innings while not factoring in the decision of an 8-5 victory over Philadelphia on July 11. The right-hander, who has made six relief appearances since, is 6-6 with a 4.00 ERA in 16 starts this season.

He's 5-6 with a 5.86 ERA as a starter against the Cubs.

Anthony Rizzo is 14 for 25 with 10 RBIs in the last seven games, and 3 for 5 with two homers and a double against Vogelsong.

Brandon Belt and Brandon Crawford each hit two-run homers in the opener.

Crawford has hit seven of his career-high 19 home runs and recorded 14 RBIs in his last 14 games. He's hit .343 in 13 career games at Wrigley Field.

Teammate Nori Aoki is batting .176 in nine games since missing a little more than a month with a fractured fibula, but is 4 for 9 against Lester.