The Cardinals go for a three-game home sweep against the slumping Pirates, who will again try to secure their first winning season in 21 years Sunday.
After taking Friday's opener 12-8, St. Louis (82-60) moved one-half game ahead of Pittsburgh (81-60) and into first place in the division with Saturday's 5-0 victory. David Freese homered and drove in two runs for the Cardinals, who have averaged 5.4 runs during a 6-3 stretch against the Pirates.
"We've been back-and-forth with them all year," winning pitcher Adam Wainwright said. "Any time you can win against them, it's a big win."
Pittsburgh is on the verge of a season worst-tying fourth consecutive defeat after going 7 for 34 (.206) with runners in scoring position during its last three games. While they have ended their run of 20 consecutive losing seasons, the Pirates are still seeking their first winning campaign since going 96-66 in 1992.
"We need to step it up, to get going again," said Andrew McCutchen, who had two of the team's three hits Saturday. "We've just got to keep battling."
All-Star third baseman Pedro Alvarez is mired in a 4-for-35 slump for the Pirates, who have dropped eight of 13. Russell Martin is 7 for his last 50.
The Cardinals will try to increase their lead behind rookie Michael Wacha (2-0, 3.20 ERA). The right-hander allowed three hits over six scoreless innings in Tuesday's 1-0 loss at Cincinnati, his first start in more than three weeks.
"He was very impressive," manager Mike Matheny said. "When you put guys in that kind of situation, you never know how they're going to react. He stepped up."
Wacha struck out four over two scoreless innings of relief in a 5-1 loss to Pittsburgh on Aug. 14, his only appearance in the series.
The Pirates counter with Charlie Morton (7-3, 3.00). Since yielding season highs of five earned runs and 10 hits in six innings in a 13-0 loss to St. Louis on Aug. 1, Morton has gone 4-0 with a 1.74 ERA during a six-start stretch.
"Charlie has gotten to a very good place," manager Clint Hurdle said.
The right-hander is looking to win a career-high fourth consecutive outing after yielding two runs - one earned - over seven innings in a 5-2 victory at Milwaukee on Monday.
"He is really good," Brewers manager Ron Roenicke said of Morton. "He throws a great sinker and pounds the right-handers in with it. It's always down in the zone. He's got a good curveball and a good changeup. That's a really nice pitcher they have."
Morton, 0-5 with a 5.68 ERA in his last seven outings versus St. Louis, can't be looking forward to facing the Cardinals again. He, however, only surrendered two runs in six innings in his last matchup, a 4-3, 14-inning road loss Aug. 13.
Morton has had a rough time against several of St. Louis' hitters, including Yadier Molina (8 for 18 with four doubles), Jon Jay (6 for 14) and Carlos Beltran (6 for 15). Molina is 5 for 12 with a homer, two doubles and four RBIs in his last three games against the Pirates.
McCutchen, a career .340 hitter at Busch Stadium, is 24 for 59 (.407) with three homers, nine RBIs and 10 runs in his last 16 road games.