The Pittsburgh Pirates sent a message to the National League Central-leading St. Louis Cardinals on Monday. By the end of Tuesday the Pirates hope to be the ones sitting at the top of the division, as they play a doubleheader against the Cardinals at PNC Park.

Pittsburgh opened this pivotal five-game series in rousing fashion on Monday, as Francisco Liriano pitched seven strong innings and Pedro Alvarez clubbed a three-run homer in the opening frame in the Pirates' 9-2 rout.

Pittsburgh, which hasn't had a winning season since 1992, is now 20 games over .500 and within a half-game of the first-place Cardinals.

Liriano (11-4) allowed a run on four hits and had eight strikeouts. The lefty won for the sixth time in his last seven decisions and moved to 6-1 at home this season.

"He continues to pitch well, be very aggressive and have confidence on the mound," Pirates manager Clint Hurdle said. "The changeup and slider continue to come into play. He's just been very solid, very professional."

Jake Westbrook (7-5) was charged with four hits and four runs over five innings to fall to 1-8 in his career against the Pirates.

"He just didn't have a feel at all for his fastball," Cardinals manager Mike Matheny said. "He tried to get a hold of his location and it took him awhile. It took a lot for him to get through five (innings), but the damage had been done already."

Matt Carpenter and Shane Robinson each drove in a run for the Cardinals, losers of four in a row for the first time since Aug. 28-31 last year.

Getting the call in the first game for the Pirates will be righty A.J. Burnett, who is 4-7 with a 2.96 ERA. Burnett did not get a decision on Thursday in Washington, but allowed just one earned run in seven innings.

He beat the Cards earlier in the year and is 7-5 with a 3.87 ERA in 13 starts against them.

St. Louis will oppose Burnett with righty Lance Lynn, who snapped a two-game losing streak his last time out. Lynn beat the Philadelphia Phillies on Thursday, limiting them to a run and five hits in seven innings, as he improved to 12-5 to go along with a 3.98 ERA.

Lynn is 4-1 lifetime versus the Pirates with a 4.23 ERA in eight games (6 starts).

Tyler Lyons will be recalled to start the second game for the Cardinals. Lyons is 2-3 with a 5.51 ERA in six starts this season, but was jettisoned to Triple-A in June after going 0-3 with a 8.68 ERA in his last four starts.

The Pirates, meanwhile, haven't named a starter for the nightcap, but the likely choices are either Brandon Cumpton or Stolmy Pimentel, two right- handers, who both pitched in a doubleheader on Thursday for Triple-A Indianapolis.

Pittsburgh is 4-2 in six games against the Cardinals this season.