Both teams held the lead in the Central earlier this season and were still on the fringes of contention after the All-Star break, but have since collapsed while the first-place Milwaukee Brewers have opened up leads of 12 1/2 games on the Reds and 13 1/2 on the Pirates.
Milwaukee leads second-place St. Louis by 6 1/2 games.
The Reds come home after dropping two of three in Washington, including the series finale Thursday when Jesus Flores' first home run of the season supported a gem by Jordan Zimmermann as the Nationals won, 3-1.
Bronson Arroyo (7-10) allowed three runs on seven hits over six innings. He walked two and struck out three and has not recorded a win since June 25.
Brandon Phillips knocked in the lone run for the Reds, who stranded 10 and went 0-for-7 with runners in scoring position.
On Wednesday in Pittsburgh, Allen Craig finished 4-for-5 with two home runs and three RBI, as St. Louis avoided a sweep with a 7-2 victory over the Pirates in the finale of a three-game series.
Jose Tabata's two-run shot was the lone offense for the Pirates, who have lost four of six despite winning the set.
Paul Maholm (6-14) was touched in defeat for three runs on eight hits over five full frames.
Cincinnati starts Texas-born Homer Bailey, who's 4-1 in six starts since opening the season at 3-4.
The former first-round draft pick - seventh overall in 2004 - is unbeaten in his career against the Pirates, holding a 5-0 record after six starts with a sterling 1.52 earned run average across 47 1/3 innings.
He was a 13-1 winner over San Diego in his most recent start on Aug. 13, allowing a run on six hits in seven innings while lowering his 2011 ERA to 4.43.
The Reds are 4-6 in Bailey's last 10 starts.
The Pirates counter with early-season ace Kevin Correia, who's dropped three straight decisions and five of six since getting to 11-6 in July 3.
The Californian, who'll turn 31 on Aug. 24, last won on July 28 in Atlanta, where he allowed an earned run on nine hits in 6 1/3 innings of a 5-2 triumph.
In losses since to the Chicago Cubs, San Diego and Milwaukee, he's surrendered 22 hits and 13 runs in 14 1/3 innings.
Lifetime against the Reds, Correia is 7-1 over 14 appearances - nine starts - with a 4.24 ERA in 57 1/3 innings.
The Pirates own a sizeable 7-2 advantage in the season series between these clubs.