The Reds -- who, like the Pirates, have an off-day on Thursday before kicking off the three-game set in Pittsburgh -- sat in third place in the division after a 2-0 win against the Astros on Wednesday, 6 1/2 games ahead of the Bucs.
Cincinnati has won two straight, partly thanks to the offensive exploits of second baseman Brandon Phillips.
The two-time All-Star has six homers in his last 10 games, with seven RBIs. Since moving to the leadoff spot on Aug. 17, he's 47-for-137 (.343) and has raised his average from .283 to .297.
Phillips has 18 homers overall.
"I'm just swinging the bat," he said. "I'm feeling comfortable at the top of the lineup and am just trying to get things done. I'm going up there having a good time."
Phillips and the rest of the Cincinnati lineup will be up against Pirates lefty Jeff Locke, who continues to search for his first Major League victory.
He struggled with command in his first two big league starts.
"The first [start], I didn't really know what to expect, didn't know how to harness the emotions," Locke said after his second outing, a loss against the Dodgers. "Today I wasn't nervous at all. I just left a lot of pitches up and got into a lot of deep counts."
The 23-year-old is expected to be on a limit of 75-80 pitches, as this marks the first season that he has pitched into September.
Reds: Volquez looking for first win since return
Cincinnati will send Edinson Volquez to the hill on Friday, as he tries to earn his first win since returning from Triple-A.
But Reds manager Dusty Baker was pleased with the right-hander's previous outing on Saturday, when he gave up five runs against the Brewers in 6 2/3 innings.
Volquez is 1-0 with a 3.44 ERA in his career against the Pirates.
Pirates: Hughes finally gives in
Right-hander Jared Hughes allowed just four singles and no runs in his first eight Major League appearances before giving up a run on two hits and a walk in one inning on Wednesday.
Pittsburgh's last six games of the season will come against NL Central foes -- three at home against the Reds and three in Milwaukee. Entering Wednesday, the Pirates are 36-38 against the division this season.
The Pirates have won eight of the 12 meetings between the two clubs this season.
Drew Stubbs (38 stolen bases and 92 runs) is trying to become just the fifth Reds player since 1900 to record 40 stolen bases and 100 runs in a season (Joe Morgan did it six times, Bob Bescher did it twice, Bobby Tolan and Eric Davis did it once). He would also be the first Reds player with 40 steals in a season since Deion Sanders had 56 in 1997.
Though the Pirates won't hit 2 million in attendance this year, this 2011 attendance will move into fourth place in franchise history on Friday. The club has drawn 1,850,651. The current fourth-place mark for season attendance is 1,866,713.