Getting Adam Wainwright on track could prove especially key if they want to remain there.
With August behind him, Wainwright tries to avenge last week's defeat to the division rival Pirates on Tuesday night.
St. Louis (74-63) extended its winning streak to three Monday as Matt Holliday followed Kolten Wong's tying pinch-hit two-run homer with an RBI single in the seventh inning of a 5-4 victory.
The Cardinals climbed one game ahead of Milwaukee, which lost Monday, and three in front of Pittsburgh (71-66) for the division lead.
"Whenever you're in first place, it means a lot, especially at this time of year," Monday's starter Lance Lynn told MLB's official website. "When it's all said and done, we want to be in first place at the end of the month."
St. Louis now turns to Wainwright, who went 2-4 with a 5.17 ERA last month. The All-Star right-hander is looking to avoid dropping three consecutive starts for the first time in nearly two years after losing 3-1 at Pittsburgh on Wednesday.
Wainwright (15-9, 2.59) has allowed 32 runs over his last nine starts after surrendering 26 in his first 18.
"Baseball is a weird, funny game. It can be very frustrating," he said. "Over the last however many starts it's been, if it's not one thing, it's another. Really, my arm has felt better. I have been going through a dead-arm phase, and everybody does. But you have to find ways to get outs.
"It has been a grind, and I'll just continue to go out there and battle my tail off until things click back into place. ... I'm ready to move on to September."
Wainwright is 4-2 with a 1.24 ERA over a seven-start stretch against the Pirates, including playoffs.
Andrew McCutchen went 2 for 5 with a homer Monday and combined with Josh Harrison for four runs, but Pittsburgh went 1 for 10 with runners in scoring position. The Pirates have lost 10 of their last 12 regular-season games at St. Louis.
"It's a game we should have won, that's how I look at it," McCutchen said. "We can't let ones like this get away."
Pittsburgh will try to bounce back behind Jeff Locke (6-3, 3.51). The left-hander allowed one run over 7 1-3 innings opposite Wainwright on Wednesday, giving him a 4-0 mark and 2.90 ERA over his last five starts.
"I've just been focused since returning here on being strong and healthy down the stretch, to give this team a chance to move forward," he said.
Locke is 2-1 with a 2.70 ERA in four starts against the Cardinals. Holliday is 5 for 11 with a homer in their matchups, while Matt Carpenter and Jhonny Peralta are a combined 0 for 12.
Holliday has hit safely in seven straight against the Pirates, going 10 for 26 with four extra-base hits and nine RBIs. He's 7 for 11 with three homers and 12 RBIs over his last three overall.
"I'm OK with him going off all month long," Lynn said. "This stretch, I'd like for it to be like a 28- to 45-game stretch. If he can keep doing what he's doing, that's a big boost."
The Cardinals activated reliever Jason Motte from the 15-day disabled list. The right-hander, on the DL due to a lower back strain since Aug. 2, is 0-0 with a 4.91 ERA in 24 games this season.