Having closed the gap on one division rival, the Pittsburgh Pirates now hope to distance themselves from another.

A four-game series that could help decide home field for the NL wild card - and potentially more - gets underway Tuesday with a day-night doubleheader between the Pirates and visiting Chicago Cubs.

Pittsburgh (86-56) is in position to host the wild-card game for a third straight year but has its eyes on a bigger prize. The Pirates have pulled within 2 1/2 games of first-place St. Louis in the NL Central with a 7-3 run they began by winning two of three from the Cardinals from Sept. 4-6.

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"We try to keep the mentality of just taking care of our game, but you can't help being aware (of the standings)," pitcher Jeff Locke told MLB's official website.

Though the Pirates host St. Louis for three games to conclude September, they still can't look past a Cubs team they'll face seven times before then. Chicago (82-60) trails Pittsburgh by four games and is 39-32 on the road, the majors' second-best winning percentage behind the Cardinals.

"Four one-game winning streaks would be great," Cubs manager Joe Maddon said. "If you start getting caught up in that big thing, it could really mess your head up. You just play that game and move on."

Chicago could be accused of looking ahead after consecutive losses at lowly Philadelphia that followed a 7-1 stretch.

Chris Coghlan finished 4 for 5 in Sunday's 7-4 loss to become the first Cubs player since 1950 with a home run and two triples in a game. He's 10 for 25 through the first six of Chicago's 11-game trip.

The Cubs draw another challenge with Gerrit Cole (16-8, 2.54 ERA) taking the mound in the opener on nine days' rest from perhaps his best performance of the season - seven scoreless innings of two-hit ball in a 7-1 win over the Cardinals on Sept. 6. It was the latest successful September effort for the Pittsburgh ace, who is 9-2 with a 2.95 ERA in 13 career starts during the month.

Cole has been quite successful against the Cubs as well, winning his first six starts behind a 2.92 ERA before allowing two runs in six innings of a 4-1 road loss May 16. He yielded one unearned run and three hits over six innings in an 8-1 win at Wrigley Field on April 29.

Kris Bryant is 2 for 3 against Cole and batting .333 with two homers and seven RBIs over a seven-game hitting streak. Anthony Rizzo (5 for 11) and Starlin Castro (5 for 13) have also hit the right-hander well.

Jason Hammel (8-6, 3.59) gets the call for Chicago in the opener and seeks to win consecutive starts for the first time since June 1 and 6. The righty fanned six while allowing three runs in six-plus innings of an 8-5 decision over St. Louis on Sept. 8.

Hammel halted a three-start losing streak against Pittsburgh by surrendering four hits in eight innings of a 4-0 home win April 27. He was reached for three earned runs in a 4-3 defeat at PNC Park five days earlier.

Josh Harrison is 1 for 11 off Hammel but 9 for 19 over his last four games, and capped a stirring comeback with an RBI single in the 11th inning of Sunday's 7-6 triumph over Milwaukee. The Pirates scored six unanswered runs to erase a 6-1 deficit in the bottom of the fourth.

The nightcap pits a pair of left-handers coming off strong starts in Pittsburgh's J.A. Happ and the Cubs' Jon Lester.

Happ (5-1, 1.79) was tagged for four runs and nine hits by Chicago in 4 1-3 innings to lose his Pirates debut Aug. 4. He's posted a 1.00 ERA in six games since and won a fifth straight start by allowing two runs over six-plus innings Wednesday in Cincinnati.

Lester (9-10, 3.50) held St. Louis to a run and two hits over seven innings Wednesday, but was denied a win when the Cardinals scored three times off Chicago's bullpen in the eighth. The veteran did earn a victory when limiting Pittsburgh to a run in seven innings May 16.

Happ is 1-3 with a 6.04 ERA in five meetings with Chicago, with Rizzo 4 for 6 with a home run and two doubles off him and Castro 4 for 9 with a pair of doubles.