Cueto lasted just eight pitches after that. He left his Game 1 start against San Francisco on Saturday night in the first inning because of back spasms, then the Reds hung on to beat the Giants 5-2 behind their stellar bullpen.
"I feel really proud about my team. I feel proud about the pitchers," Cueto said. "They all came in and did their job."
The Reds said he is day to day. The right-hander threw a second strike to No. 2 hitter Marco Scutaro and walked off the mound in obvious pain. A trainer and manager Dusty Baker rushed out to check on him, and the 19-game winner came out moments later.
Now, the Reds hope to get him back this series. Cueto wants to see how he responds Sunday.
"I really feel better right now," Cueto said after the game. "This is my first time it happened."
He retired leadoff man Angel Pagan on a strikeout. During the at-bat, Pagan stepped out of the batter's box and was granted time. Cueto apparently didn't see it and continued his motion, but Baker said pitching coach Bryan Price had alerted him to Cueto's discomfort beforehand.
Cueto threw eight pitches and six strikes for the earliest postseason exit by a starter since Atlanta's John Thomson lasted one-third of an inning in Game 3 of a 2004 NL Division Series against Houston. Thomson came out with a sore muscle in his left side.
"When Johnny went down, I was like: 'Gosh, oh no, we're done. Why? Why? Why?'" Brandon Phillips said. "We're out there talking, and we're like, 'Let's win this for Johnny.'"