Pittsburgh's best chance to reel in the NL Central leaders starts with Friday night's series opener at Busch Stadium, a ballpark kind to the Cardinals and not so much to the Pirates this year.
Losers of four straight and 6 1/2 games back with a month to play, the Pirates (79-53) badly need a series win, something they haven't done in St. Louis since April 26-28, 2013.
Pittsburgh is 4-18 at Busch Stadium since then, including a 1-5 mark this season.
The Pirates still hold a four-game lead over the Chicago Cubs for the top wild-card spot despite losing three straight in Milwaukee, including Thursday's 5-3 loss.
"Our focus needs to be on playing better," manager Clint Hurdle said. "We got outpitched, outhit and out-defended three straight games."
The Pirates will have one of their hottest pitcher's on the mound Friday.
J.A. Happ (3-1, 1.98 ERA) has flipped around his season since coming to the Pirates via a trade with Seattle on July 31.
He struggled to a 4-6 record and 4.68 ERA in 20 starts with the Mariners, but he has won each of his last three starts with the Pirates with an ERA of 0.51 in victories over Arizona, Miami and Colorado.
The bad news is Happ's 1-8 record and 6.79 ERA in 10 starts against the Cardinals, though he hasn't faced them since 2012. He's especially bad in St. Louis, going 0-3 with a 12.34 ERA in three career starts there.
Brandon Moss (6 for 8) and Yadier Molina (6 for 15) have hit Happ hard, but Mark Reynolds is 0 for 16 with eight strikeouts against him. Jon Jay is 5 for 11 against Happ and is expected to be activated off the 15-day DL before the series opener.
Jay, out since July 1 with a stress reaction in his left wrist, is one of several key contributors the Cardinals expect back in September, joining outfielders Matt Holliday (right quad strain) and Randal Grichuk (right elbow strain), and first baseman Matt Adams (right quad strain).
"That's a pretty good boost when you start talking about the guys who we could potentially be bringing back here," manager Mike Matheny told MLB's official website. "We're talking about some of the key components of our club."
Pittsburgh is expected to reinstate Andrew McCutchen to the lineup after he sat out Thursday with what Hurdle called left knee soreness.
While the Pirates have fallen back, St. Louis (86-47) is making a push for its third straight division title with nine wins in 11 games.
The Cardinals, who are a major league-best 48-20 at home, will send Carlos Martinez to the mound to try and rebound from Wednesday's 4-3 loss to Washington that snapped a four-game win streak.
After pounding Martinez (13-6, 2.91) for seven runs over 5 1-3 innings in a 7-5 win on May 9, Pittsburgh didn't do much against him in losses of 4-1 on July 9 and 4-3 on Aug. 11.
Martinez - pitching on eight days' rest due to back tightness he experienced in a 5-3 win over Arizona on Aug. 27 - held the Pirates to three runs in 15 1-3 innings between the two wins.
Gregory Polanco has eight hits in 11 at-bats against Martinez, going 5 for 8 with two doubles and a triple this season.
St. Louis rookie Stephen Piscotty is hitting .419 with 11 RBIs during his career-best 10-game hitting streak.