The Reds dropped the first two games, but pulled out a victory on Wednesday when Joey Votto smacked the go-ahead solo home run in the bottom of the sixth inning to send the hosts to a 3-2 win.
Cueto, who turned 25 in February, was a nine-game winner as a rookie in 2008 and has since won 11 and 12 games in 2009 and 2010.
He picked up his seventh win of 2011 and the 39th of his career on July 31, when he tossed a three-hit shutout with six strikeouts to defeat San Francisco, 9-0.
Attempt No. 1 at win No. 40 fell short when he was touched for five runs on seven hits in 3 2/3 innings at Wrigley Field against Chicago.
He is 4-3 in his last 10 starts, in which the Reds are 6-4.
Cueto is winless in two career starts against the Rockies, having allowed three earned runs on seven hits in nine innings.
For Colorado, righty Jhoulys Chacin takes his first crack this season at double-digit victories.
The 23-year-old Venezuelan, who was 9-11 in 28 appearances last season, improved to 9-8 this year with a 15-7 defeat of the Washington Nationals in his last start Aug. 6.
The victory snapped an eight-start drought for Chacin, who'd been 0-4 since defeating San Diego on June 15 in Denver.
The Rockies are 3-7 in his last 10 starts, though Chacin has allowed three runs or less six times and only one run four times.
He is 1-0 in three career meetings with the Reds, having allowed three runs on seven hits in 9 2/3 innings.
Colorado took five of seven from the Reds last season.