Would-be National League earned run average leader Johnny game series against the Washington Nationals.
Cueto, a 25-year-old Dominican and 12-game winner last season, has pitched to a 1.94 ERA across 120 1/3 innings so far this season, but is 1 2/3 innings shy of what he needs to qualify for the league lead.
Instead, the ERA race is led at 2.47 by San Francisco's Ryan Vogelsong.
Cueto pitched seven scoreless innings of three-hit ball in his last outing, a 2-1 defeat of the Colorado Rockies on Aug. 11. It came one start after he was touched for five runs in just 3 2/3 innings of an 11-4 loss to the Chicago Cubs.
In his last 10 starts, Cueto has allowed three earned runs or less nine times and zero or one earned run six times. The Reds are 6-4 in that span.
He is 3-2 in five career starts against Washington.
The Nationals reply with 25-year-old lefty Ross Detwiler, who again aims for a first win since his season debut in early July.
Detwiler, who won one decision apiece in 2009 and 2010, defeated the Chicago Cubs on July 5 with 5 1/3 innings of two-run ball.
He subsequently made five straight appearances in relief, then returned to starting and has dropped decisions to Colorado and the Cubs while giving up 12 hits and five runs in 10 innings.
Detwiler has one career start against Cincinnati and lost after allowing three runs on five hits in six innings.
On Tuesday, Michael Morse went 2-for-4 with a solo home run, an RBI double and two runs scored to lead the Nationals to a 6-4 victory in the series opener.
Chien-Ming Wang (2-2) gave up four runs on seven hits over 6 1/3 innings to earn the win in his first career start against the Reds. He issued only one walk and did not strike out a batter. Drew Storen worked a 1-2-3 ninth to notch his 32nd save of the season.
Mike Leake (10-8) yielded six runs -- five earned -- on seven hits while striking out five and walking one.