This time he stayed in for a few more pitches and it put the Pittsburgh Pirates in a deep hole.
Corey Hart and Aramis Ramirez both went 3 for 4 with home runs, and Karstens left for the second consecutive time with an injury as the Milwaukee Brewers beat the Pirates 9-3 on Friday night.
The Brewers took a 2-0 lead in the first inning and had a runner on first with Corey Hart at the plate. Karstens threw a slider to the Brewers slugger and felt the same pain that caused him to leave his last start on Aug. 25.
A couple pitches later Hart hit his 25th home run to give Milwaukee a 4-0 lead and the Brewers never were seriously threatened after that.
"If I would've known this was going to happen, I definitely would not have tried to take the ball," Karstens said. "It is not something I try and do."
Manager Clint Hurdle said Karstens passed the tests given by the team's trainers and threw a routine bullpen session in between the starts.
"It wasn't really until the sequence to Hart that we noticed something and he confirmed that after he came out that he felt something grabbing a little bit again," Hurdle said. "It was only about a three-pitch sequence where he was trying to get the ball away, he wasn't able to finish."
After Hart's homer, Jonathan Lucroy singled. The Pirates trainers went to the mound, and after talking with Karstens for a few moments he walked to the dugout finished after only 20 pitches.
"I don't want to put my team in a situation like that," Karstens said. "To kind of do that, one, it is upsetting to me and, two, it is just disappointing because I felt like I left the team down. It is kind of deflating for myself."
After the injury on Aug. 25, the Pirates described it as a left groin strain. The team said Karstens felt discomfort in his right hip flexor this time, but Karstens said it was the same feeling as he had on Aug. 25.
Pittsburgh remained one-half game behind St. Louis for the final NL wild-card spot when the Cardinals lost 10-0 to Washington on Friday night.
Milwaukee starter Mark Rogers (3-1) gave up one run in 5 1-3 innings to win his third consecutive start in what could be his last outing of the year.
"I feel great about the season," he said. "I feel like I've come a long way this year. I've battled my way back from injuries before so it's pretty gratifying to be here right now and be a part of this ballclub."
Brewers owner Mark Attanasio said on the team's television broadcast that the right-hander would be shut down, but manager Ron Roenicke refused to confirm it after the game, saying he had not talked to Rogers.
"I don't want to say one way or another whether it is or not," Roenicke said.
NOTES: The Pirates recalled RHP Kyle McPherson and OF Alex Presley from Triple-A Indianapolis. To make room on the roster, INF Chase d'Arnaud was optioned to Class-A Bradenton and 1B Jeff Clement was outrighted to Bradenton.