KANSAS CITY -- Jason Castro pumped his fist as he rounded the bases following his record-breaking homer.

Castro didn’t know until after the game that the homer was far more important than he initially thought.

The postseason hasn’t even started yet, but the Twins gathered some symbolic momentum in Sunday afternoon’s 5-4 walk-off loss to the Royals at Kauffman Stadium before the upcoming American League Division Series by emerging triumphant in a season-long battle against the Yankees.

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The Bomba Squad entered the day with 304 home runs, trailing the Bronx Bombers by one in the back-and-forth quest for the all-time home run title. New York added one with an Aaron Judge blast against the Rangers, but Minnesota rose to the challenge and triumphed with three homers, capped by Castro's blast, in Sunday's defeat, bringing the Twins’ final tally to 307 to stand alone as the most powerful team in Major League history.

The Twins finished the regular season at 101-61, falling one win shy of the 1965 club’s franchise record for most wins in a season.

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“I don’t think anybody will ever forget the Bomba Squad, and I mean that,” manager Rocco Baldelli said. “Over a six-month season, our guys just went out there and hit more home runs than any team in the history of baseball. Who knows if it will ever be broken. You never know. It’s a record, and this game has been played by a lot of great players for a very long time.”

Castro’s fifth-inning blast gave the Twins the decisive 307-306 edge, but his fist pump actually had nothing to do with that. Instead, he had entered the game with the knowledge that he needed a homer to give the Twins the most homers hit by catchers in a season in Major League history -- 44 -- and that’s what he had been celebrating.

It was only as Castro walked through the tunnel after the game that reliever Trevor May told him that his homer had delivered the Twins the home run crown.

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"So I knew that we were kind of jockeying back and forth between us and the Yankees,” Castro said. “I actually didn't know. I thought they had the lead by a few more than they did. I actually didn't know until after the game that we surpassed them on that last one. I had no idea."

Neither C.J. Cron nor Jake Cave, who hit Minnesota’s other homers on Sunday, said they knew exactly where the Twins stood with respect to the Yankees until Minnesota senior director of communications Dustin Morse told the team in the clubhouse after the game.

Don’t blame Mitch Garver for that, though. Garver said after the game that he had been counting down for weeks and was all too aware throughout Sunday’s game that the Yankees had only scored one run. When Castro hit Minnesota’s third homer of the game, Garver figured that would be enough to clinch the record, and he yelled it for all of his teammates to hear. Apparently, nobody heard him.

"I'm walking up and down the dugout,” said an indignant Garver. “Literally yelling that we have the home run record."

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Even with their two most productive sluggers -- Nelson Cruz and Max Kepler -- on the bench, the Twins wasted no time in getting the power show started in the first inning, when Cron and Cave hit back-to-back blasts off Kansas City starter Jorge López to seize a quick 306-305 lead in the home run tally and a 3-0 advantage in Sunday’s game.

“Selfishly, it's something that nobody can ever take from me regardless of what my career is like in baseball,” Cave said. “I can say, 'Hey, I contributed eight homers to the team that broke all the home run records.' At least for the time being. For me, that's really cool.”

Cave’s homer was significant, because it gave the Twins the homer lead over the Yankees, but Cron’s blast was arguably more meaningful for Minnesota, as the first baseman’s problematic bruised thumb is one of the more significant injury questions facing the Twins as they enter the postseason. In a promising sign, Cron’s line-drive shot left the bat with an exit velocity of 115.6 mph, his hardest-hit big fly of the season.

“In Spring Training, we had a lot of goals in mind,” Cron said. “I don’t think the home run record was one of them. Obviously, it’s super humbling and awesome to have, but the position we’re in now, our focus is 1,000 percent on the upcoming series. At least I hope so. I’m sure when we’re all retired and look back, and if it’s still kicking, that would be cool.”

As the Royals and Twins did battle through the middle innings, the Yankees punched through the equalizer at Globe Life Park, courtesy of Judge’s third-inning shot off former Twins starter Lance Lynn, which pulled the clubs even at 306 homers apiece.

That tie only survived 40 minutes before the Twins again pulled ahead on Castro’s shot -- this time, for good.

But the single-season record wasn’t secure until an hour and a half later. Only seconds before the Royals walked off on Brett Phillips’ sacrifice fly in the bottom of the ninth, Texas reliever Jose Leclerc finished off the Yankees at Globe Life Park, officially securing the home run crown for the Twins.

“I think the way we've been swinging the bats all season, it's just been such a special year, and to cap it off like this is kind of the cherry on top,” Castro said.