Royals manager Ned Yost said after the game that Sunday was Keller's last start of the season.
"We want to get Eric Skoglund one more start next weekend," Yost said. "It's more beneficial for him to get another start than Keller. Keller has had a fantastic season."
Keller's only jam came in the sixth. With one out, he walked Jeimer Candelario and Christin Stewart. Both runners moved up on a wild pitch, but Keller then struck out Nicholas Castellanos on a slider down and away, and jammed Niko Goodrum, who popped out to short.
"Castellanos is tough, and he's burned us a couple of times this series," Yost said. "Keller made a good pitch to get through that."
"Just go after him," Keller said. "We knew he would be aggressive. He's been aggressive all series. The tying run was essentially on second, we didn't want to give him anything good. Threw some pretty good sliders there.
"Big moment right there, especially after the team gave me the lead."
Meanwhile, Kansas City's offense mustered just enough support. Adalberto Mondesi took a 3-2, four-seam fastball from Daniel Norris in the first inning and drove it over the left-field fence for his 12th home run.
Royals closer Wily Peralta got his 13th save and ended the game by striking out Jim Adduci, which Peralta did on Friday as well. Peralta already had allowed a run and had the tying run on second.
"At times he'll walk a bit of a tightrope, but he's been perfect, 13-for-13," Yost said of Peralta. "He doesn't panic. He just keeps making pitches."
On Friday, Peralta started out with one fastball against Adduci and then went with mostly changeups before getting him on a slider.
"Two straight times I had to get him," Peralta said, smiling. "Last time we started with one fastball and two changeups. This time we decided to double up with the fastball and he was late both times. Then I got a changeup over that was high but he didn't get it. Very happy for that."
UP NEXT After an off-day Monday, the Royals will play their final two road games of 2018 starting Tuesday in Cincinnati at 5:40 p.m. CT. Left-hander Eric Skoglund (1-5, 5.60 ERA) will start for the Royals, while right-hander Matt Harvey (7-9, 4.92) will go for the Reds. Skoglund threw six scoreless innings on three hits Sept. 18 against the Pirates.