Arroyo, who pitched out of a first-inning jam, gave up one run in seven innings and the Reds beat the Braves 3-1 on Friday for their fifth straight win.
The Braves, who began the day four games behind Colorado in the NL wild-card race, have lost three straight.
The Braves did not score after loading the bases with no outs in the first. Brian McCann hit into a double-play grounder that forced Matt Diaz out at the plate. Adam LaRoche ended the inning with a fly ball to left field.
"It's just frustrating," McCann said. "We had our chance in the first. I grounded into a double play and kind of killed the rally. Then it seemed like every ball we hit hard was right at them."
Manager Bobby Cox was ejected for second straight game, and the seventh time this season, to extend his major league record to 150.
The Reds, coming off a four-game sweep of Pittsburgh, matched a season high with their fifth straight win.
"We obviously don't have a chance for the playoffs, but we have an opportunity to look at what we will have next year," Arroyo said.
Brandon Phillips says it is not too late for the Reds (61-73) to avoid a losing season.
"We're just trying to get as many wins as possible," Phillips said. "If we can get to .500, that would be a positive thing for us."
Arroyo (12-12) gave up six hits and one run in seven innings. He shut out the Braves for five innings before giving up Nate McLouth's homer in the sixth. He has lasted at least seven innings in seven straight starts. The right-hander was only 1-2 in his last six starts despite a 1.99 ERA.
"After that first inning, he got on track and dealt the rest of the way," said Reds manager Dusty Baker.
Arroyo's only other win in the seven-game span was a two-hit shutout of Washington on Aug. 13.
"After pitching well several games in a row and not getting the win, to finally get over the hump and get a win feels really good," Arroyo said.
Jonny Gomes' 17th homer in the second gave Cincinnati a 1-0 lead.
Francisco Cordero pitched the ninth for his 31st save.
Arroyo beat Derek Lowe (13-9), who gave up seven hits and three runs in seven innings.
Kenshin Kawakami pitched a perfect eighth in his first relief appearance for Atlanta after 25 starts.
"Our pen needs some help right now," Cox said. "We've got some guys that need a little bit of rest so he's going to have to carry a little bit of load out there."
Tim Hudson's return from elbow surgery left the Braves with six starting pitchers, allowing Cox to move Kawakami to the bullpen.
The Reds scored two runs in the sixth. Joey Votto walked and scored on Brandon Phillips' double to center field. Scott Rolen's single to center drove in Phillips.
McLouth came off the 15-day disabled list after missing 17 games with a strained left hamstring.
Plate umpire Brian Gorman ejected Cox in the fourth inning.
Gorman called Yunel Escobar out for running outside the base path on the infield grass as he tried to beat Arroyo's throw to first. Arroyo's throw hit Escobar. Cox argued the call.
"Unbelievable," Cox said of the call.
Cox said Escobar had to be in line with Arroyo's throw to first base if Escobar was to run across the base.
"You can only be where you are," Cox said. "The ball had to hit him no matter where he was."
Escobar appeared to be injured while stretching for first base. X-rays were negative.
Cox said Escobar's status is day to day. Escobar nodded when asked if he expected to miss two or three days.
Omar Infante moved from left field to shortstop to replace Escobar.
Cox also was ejected in Thursday night's 8-3 loss at Florida. ... McLouth did not start but entered the game in the fourth inning after Escobar's injury. ... Wladimir Balentien's first-inning triple was the first of his career in 472 at-bats. ... The Reds opened a 10-game road trip and a streak of games on 17 consecutive days.