The Pittsburgh Pirates had their sights set on NL Central-leading St. Louis before the Chicago Cubs forced them to concentrate on the rear view mirror.

After dropping three of four against the Cubs this week to put their lead in the wild-card race in a precarious position, the Pirates now have to deal with a pair of Cy Young candidates in the first two of a three-game series against the Los Angeles Dodgers.

With Zack Greinke on the mound for the Dodgers in Friday night's opener, Pittsburgh begins the Herculean task of getting this make-or-break 10-game trip off to a good start.

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The Pirates (87-59) sit second in baseball's toughest division, but even though St. Louis remains within striking distance, they should be more concerned with the Cubs, who pulled two back of the wild-card lead with a 9-6 victory Thursday at PNC Park.

Chicago, which owns the tiebreaker by virtue of a 10-6 record against Pittsburgh this season, rallied with a six-run fifth inning.

"We've got to play better baseball moving forward," manager Clint Hurdle said of losing the series.

Pittsburgh and Chicago are both in a safe spot to make the playoffs, but the Pirates would obviously prefer hosting the wild-card game instead of playing it at Wrigley Field, where they're 2-4 this season and close their trip with three games Sept. 25-27.

The club also took a hit Thursday when rookie shortstop Jung Ho Kang suffered a knee injury when Chris Coghlan slid into him trying to break up a double play. Kang, hitting .287 with 15 home runs, was to have an MRI but may be lost for the season.

"They outplayed us," second baseman Neil Walker said, "then the icing on the cake is they knocked out one of our best players."

Greinke (17-3, 1.61 ERA) and teammate Clayton Kershaw could certainly help matters for the Cubs in the first two of this series. Greinke is looking to become the first pitcher since Roger Clemens in 2005 to maintain a sub-2.00 ERA for an entire season, while Kershaw has won nine straight decisions and owns a minuscule 0.96 ERA over his last 12 outings.

Greinke hasn't faced the Pirates this year and has struggled against them, losing his previous two outings to fall to 5-3 with a 5.37 ERA over nine career starts.

Those numbers, however, appear comical compared to the season Greinke is having. After tossing eight scoreless innings in a 4-3 win over Arizona on Sunday, the right-hander also has a shot to become only the third since the mound was lowered in 1969 to post an ERA below 1.60. Greg Maddux (1.56 in '94) and Dwight Gooden (1.53 in '85) are the others.

"Maybe," Greinke said when asked if this is the best he's pitched. "I know what I'm doing more now. Maybe more mentally aware of how things work than earlier in my career."

The first-place Dodgers (84-61) hold a 7 1/2-game lead over San Francisco in the NL West after winning 17 of 22 since a five-game skid in late August.

Tasked with slowing Los Angeles will be Jeff Locke (8-10, 4.43), who has bounced back from a poor outing at Milwaukee on Sept. 2 with two decent starts. Locke allowed three runs - one earned - over five innings in a 3-1 loss to Cincinnati on Sept. 7 before tossing 6 1-3 of one-run ball in a 10-2 rout of the Brewers on Saturday.

The left-hander is 1-2 with a 3.94 ERA in three career starts against the Dodgers, but he hasn't faced them since picking up that lone win by tossing seven innings in a 3-0 home victory on June 14, 2013.