Cordero, the former Reds closer who was acquired from the Blue Jays in a trade last week, gave up three runs in the ninth for the second consecutive game and has blown two saves in two chances with the Astros.
"We're right there," Astros left fielder J.D. Martinez said. "I felt like [Tuesday] and tonight, the fact we were able to come back in that last inning, I'm sure a lot of us thought that was it. That's baseball, and it's frustrating but I'm sure we'll bounce back."
By scoring three runs in the ninth inning for the second game in a row, the first-place Reds swept the series and have won a season-high seven straight games, while the last-place Astros have lost a season-high-tying nine games in a row. Houston has lost 22 of its last 24 games overall.
The Astros dropped to 33-4 in games in which they led going into the ninth inning, with two of those losses coming in the final two games of the Reds series. Houston has been outscored 48-23 in the ninth inning this year.
Astros starter Bud Norris, who's suddenly become the "old man" in the rotation following Tuesday's trade of Wandy Rodriguez, pitched like he did early in the season when he was so effective. He went seven innings and allowed only five hits and one run, striking out seven, but he still hasn't won since May 21.
"I needed to make some adjustments," said Norris, who gave up nine runs in his previous start five days earlier in Arizona. "I struggled a little bit in San Francisco and I struggled a little bit in Arizona, but it felt good to come home and pitch like that. I knew I needed to make some adjustments, and I did."
Norris gave the Astros their third consecutive quality start in the series, with Houston starters posting a 2.25 ERA in 20 innings pitched in the Reds series. Astros relievers had a 15.43 ERA in seven innings in the series.
"Bud fell right in line, and in all three of these we had an outstanding outing and starting pitching did a great job," Astros manager Brad Mills said. "All those guys were exactly what we needed. Obviously, leaving the runners at third and struggling with runners in scoring position, that definitely was one thing that was our Achilles' heel today."
The Astros were 2-for-15 with runners in scoring position, including no hits in their first 11 chances with runners at second and third. They had two runners on base against Reds starter Homer Bailey in the second, third, sixth and seventh and couldn't score.
"This team doesn't quit, and thank goodness for that," Reds manager Dusty Baker said. "That eighth wasn't a very pretty inning."
Cincinnati held a 2-0 lead in the eighth inning before reliever Logan Ondrusek gave up three runs (two earned). Jose Altuve led off with a double and was at third base with two outs when Scott Moore ripped a double to right field, putting the Astros on the board and snapping Houston's 0-for-11 funk with runners in scoring position.
Martinez followed with a double off the wall in left-center to tie the game, but he went to third on an errant throw to the infield by Ryan Ludwick and was able to scurry home with the go-ahead run on the play when first baseman Todd Frazier threw the ball into the stands.
"I saw the cutoff guys and I was assuming the throw was going to third, and once I saw it going to second I was like [I could make third]," Martinez said. "I kind of peeked back a little bit and saw Frazier was nowhere near it, and I just kind of took off."
Cordero (0-2 with the Astros) came on in the ninth to protect a 3-2 lead and allowed a leadoff double to pinch-hitter Xavier Paul and walked pinch-hitter Brandon Phillips with one out before Stubbs launched his double to the gap in left field to put the Reds on top. Cordero was pulled from the game, and Jay Bruce hit an RBI single off Fernando Abad to stretch the lead to 5-3.
Cordero didn't make himself available to the media after the games, and Mills was non-committal when asked if the veteran was going to stay in the closer role.
"The best way I can answer that is he threw 29 pitches [Tuesday] night and 28 tonight, and he's probably not going to be the closer [Thursday] because that's a lot of pitches," Mills said. "Give us some time moving forward, and we'll go from there."