Francisco Liriano is a big reason why the Pittsburgh Pirates are at the top of the NL Central.

The lefty heads to the mound Saturday hoping to get the Bucs back on the winning track when they continue a three-game series against the Colorado Rockies.

Pittsburgh holds a slim half-game lead on St. Louis in the division.

Liriano has won two consecutive starts and is 6-1 over his last seven contests, the same mark he's recorded at home this year. Aside from giving up five runs in a loss at Cincinnati on July 19, Liriano has yielded two runs or less in the remainder of his last eight starts. That includes giving up one run over the last two outings, covering 14 2/3 innings in wins over the Cardinals and Nationals.

This season is a big change from last year for Liriano, who was a combined 6-12 in 2012 with the Twins and White Sox. His ERA at PNC Park is 1.61 in seven starts.

Liriano lost his only career start against the Rockies when he gave up three runs in seven innings on June 17, 2010. All three runs he allowed came in the first inning.

Jorge De La Rosa counters Liriano for the Rockies. The lefty is 2-0 over his last four starts and hasn't lost since July 5 at Arizona. De La Rosa was fortunate not to take a loss on Monday at Atlanta when he gave up 10 hits and eight runs -- five earned -- over five innings. The Rockies lost that game, 9-8, in 10 innings.

Jhoulys Chacin pitched eight strong innings and Troy Tulowitzki homered in Colorado's 4-2 win last night. Chacin (10-5), who retired the final 14 batters he faced, gave up six hits, a run and had three strikeouts.

"He was outstanding. Exactly what we needed. We need to save the pen," Rockies manager Walt Weiss said.

Tulowitzki and Todd Helton each drove in two runs for the Rockies, who snapped a four-game skid.

Gerrit Cole (5-5) allowed three hits and three runs over 5 1/3 innings. The rookie right-hander also had six strikeouts, but lost for the fifth time in his last six starts.

"I felt like we played a good game," Cole said. "We just didn't string hits together at the right times early."

Andrew McCutchen and Pedro Alvarez each knocked in a run for the Pirates, who took four of five games from the Cardinals earlier this week to take over first place in their division. The Bucs were throttled, 13-0, in the finale of that series Thursday night.

The Rockies and Pirates are meeting for the first time since Pittsburgh took four of six matchups a season ago.