"The last couple of games have been fun, stringing together those hits, especially today off Cueto," Haren said. "I thought I was going to have to give up zero or one run to have a chance. It's nice getting to him and adding on.
"It's a nice way to finish the half. We have a long road trip coming out. We've got to play some really good ball."
Cueto was 4-1 with a 4.04 ERA in his career against the Marlins before Sunday. The Reds right-hander allowed five runs (three earned) in five innings.
Haren, meanwhile, worked out of trouble and minimized damage, allowing one run on five hits with three walks and three strikeouts in six innings.
"I was able to make some good pitches and get some strikeouts," Haren said. "From there, I was in jams a couple of times and pitched out of them. All and all, it went well."
Haren, Miami's most reliable starter, improved to 7-5 with a 3.24 ERA.
"Those of us who had an opportunity to see him early in his career when he was a mid-to-upper-90s guy with a split-finger [fastball], he has somewhat remade himself," manager Dan Jennings said. "Early, he didn't have the tempo, rhythm he normally has. But he settled in there about the third. He really got it going. He held the Reds; they were 1-for-11 with runners in scoring position."
Haren, like Cueto, has been the subject of trade rumors.
The Marlins are open to moving players who aren't necessarily part of their 2016 plans, but the organization hasn't totally given up on 2015. Haren understands there is plenty of ground to make up in the second half and there is urgency.
"Time is running out," Haren said. "We've got to make a move."
The Marlins had an injury-plagued first half, especially with their rotation, as Henderson Alvarez, Mat Latos and Jarred Cosart each spent time on the disabled list. Jose Fernandez just returned from Tommy John surgery.
"Any time you lose your first three starters, it's going to be tough," Haren said.
The team also has All-Star right fielder Giancarlo Stanton (broken left hand) on the DL, and All-Star second baseman Dee Gordon out with a dislocated left thumb. Center fielder Marcell Ozuna is in Triple-A, demoted after struggling.
"You do that to any team, they're going to struggle," Haren said.