• Tiebreaker information
Cain had drifted into fair territory when he started his run.
"I actually kind of told myself in the middle there to get back to the right," Cain said. "I've been called out on that before for running inside the baseline. So I wanted to make sure that didn't happen again."
Boyer tossed toward first, but the ball hit Cain in the back and Alcides Escobar scored the lead run from third. The Royals added three more runs and took a half-game lead over the Blue Jays for home-field advantage in the postseason, pending Toronto's game with Tampa Bay later in the evening.
Twins manager Paul Molitor discussed with the umpires the possibility that Cain had drifted into fair territory. But after a consultation, the crew agreed Cain was not inside the baseline.
"The umpires got the call right," Royals manager Ned Yost said.
For maybe the first time this year, Cain, who has been hit 12 times by pitches this year, wasn't bothered by a ball hitting him in the back.
"Yeah, I'll take it," he said. "We definitely needed that run."
Cain was just coming back from a knee injury sustained on Wednesday night when he fouled a pitch right off his kneecap. Royals trainers have told him the knee will "keep barking" for about three or four weeks.
"But I'll be ready to go all out for the playoffs," Cain said. "Got those three or four days of rest before it starts."
Cain also had two doubles in Saturday's game.
"It doesn't affect me when I'm hitting," he said. "It's just when I'm in center or on the bases. I'll be OK."
Jeffrey Flanagan is a reporter for MLB.com. Follow him on Twitter at @FlannyMLB. This story was not subject to the approval of Major League Baseball or its clubs.