Although Detwiler struck out a career-high seven in six innings — his longest outing this season — the Nationals lost 2-1 on Wednesday night as Cueto pitched into the ninth inning.
Detwiler (1-3) left one inning shy of his career high. He hadn't pitched more than 5 1-3 innings this season.
"He pitched great," teammate Jayson Werth said. "Not too many times you look up there and see a lefty throw 94, 96. He had good stuff."
The only blemish for Detwiler was Joey Votto's 20th home run with two outs in the first inning on a fastball that stayed up.
"Looking at it now, throw anything but what I threw there, and hopefully he doesn't hit it out," Detwiler said.
After falling behind 2-0 going into the ninth inning, the Nationals rallied.
"He made a good pitch and got out of it," Werth said. "We were in position to win the game. I think as time goes on with these guys and this team, you keep getting your opportunities and eventually you're going to turn the corner and get it done."
"We were fortunate to get that one," Reds manager Dusty Baker said. "We squeaked that one out big time."
For most of the game, the 1-0 lead from Votto's homer looked like it would be enough for Cueto (9-5), who allowed six hits, struck out five and did not walk a batter.
Washington had runners reach third base in the second and fourth innings, but each time Cueto easily got out of the jam.
"He had a special outing tonight," Nationals manager Davey Johnson said. "Our problem was we had guys on third base with nobody out and we didn't get anybody in."
After the homer, Detwiler primarily relied on his sinker, which he was able to keep down in the zone, to keep the Reds to the one run.
Detwiler got out of a jam in the third when the Reds loaded the bases with one out. Brandon Phillips singled, Dave Sappelt doubled and Votto walked before Detwiler struck out Jay Bruce and Miguel Cairo hit a fly ball to shallow right field to end the inning.
Detwiler picked up his third straight loss despite not allowing more than three earned runs in any of his four starts this season.
"I feel like Ross has pitched well the last couple outings," Nationals shortstop Ian Desmond said. "We haven't given him very much run support."
On the other side, Cueto, who opened the game by striking out the first three batters, narrowly missed his second shutout of the season. He leads the majors with a 1.89 ERA after the outing gave him enough innings to officially qualify.
The Reds picked up an insurance run in the eighth. They had a chance to pick up a few more but left the bases loaded.
Consecutive singles by Votto and Bruce against reliever Sean Burnett put runners on the corners with no outs. Cairo grounded sharply up the middle, and Burnett snagged it and threw to third to catch Votto, who had started for home on the play. Another walk by Burnett loaded the bases.
Ryan Mattheus replaced Burnett, and Hernandez hit a grounder up the middle that was fielded by Desmond. A slight slip when Desmond fielded the ball left him unable to turn a double play, but he did throw out Hernandez while Bruce scored.
Another walk by Mattheus loaded the bases for Cueto, who grounded to second to end the inning.
NOTES: Nationals RHP Steven Strasburg, who had Tommy John surgery last year, made his third minor-league rehab start for Class A Hagerstown. Johnson said Strasburg may eventually replace RHP Jordan Zimmermann, who has an innings cap this season because of his 2009 Tommy John surgery. Johnson said Zimmermann likely has three more starts, and the manager speculated Strasburg may fill his spot on Sept. 2. ... Desmond batted leadoff for the first time since April 14. ... Phillips led off for the first time this season. ... Zimmermann (7-10) starts Thursday against Reds RHP Bronson Arroyo (7-9) in the final game of the series.