The victory ended a three-game skid by the Royals, who had lost the first two games of this four-game series.
"I just got a good pitch to hit and didn't miss it there at the end," Butler said. "It was a big pickup for the pitching staff. Obviously it's been a tough series for them, but they picked us up throughout the season and I hope that gets us going."
The Mariners, behind 7-3 after five innings, came back to tie it in the seventh. Greg Holland pitched a perfect ninth inning before Butler came out of the dugout in the bottom half.
"Billy's a special hitter," manager Ned Yost said. "He went up in that inning and said, 'I'm going to take the first pitch because I know it's going to be a slider. I want to get a really good look at it and gauge it,'" Yost said. "Then he sat on one and drove it into the stands. He's a special hitter."
Butler watched two sliders go by, then waited for a fastball and Kinney obliged. Kinney had a plan, too -- throw a sinking fastball away -- but the ball strayed back over the middle of the plate.
"I know he's their dangerous guy in the lineup. We had a plan, and I felt good out there. I had command of my pitches," Kinney said. "Actually felt real good. But that's what happens. You miss your spot to that guy, and he did just exactly what he's supposed to do. Sometimes it stinks, but you've just got to say, 'Good AB and he got me.' Maybe I'll get him tomorrow."
Butler wasn't real sure that his drive would carry over the left-field wall.
"As the night goes on, it's tougher and tougher to hit it out of here. The air gets thicker and earlier in the game. I feel like it would've gone a lot further," Butler said. "I knew at least I would've had a double for us and been on second base for a pinch-runner."
No need for that pinch-runner, the ball cleared the wall with room to spare.
Yost admitted he breathed a small sigh of relief, thanks to his starter Bruce Chen. When Chen got through the third inning, he'd already matched the total innings pitched by the Royals' previous two starters -- Jonathan Sanchez went 1 1/3 innings on Monday and Ryan Verdugo 1 2/3 on Tuesday.
And when Chen got into the sixth with a 7-3 lead, there was cause for celebration.
"You could tell after the first inning -- Bruce struck out the side -- that he was on his game today," Yost said. "It's too bad that Bruce didn't get the win, because he pitched well and deserved it."
Lorenzo Cain's two-run homer -- his second in six games since rejoining the Royals -- gave Chen that four-run lead. Earlier, Alex Gordon drilled a two-run double in the fourth. Mike Moustakas' double, Brayan Pena's groundout and Chris Getz's bunt single drove in second-inning runs.
"Ultimately, our offense has been clicking, and we have hit the ball very well," Chen said. "I think it's up to us, the starting rotation, to step it up and help our team out, because our offense is pretty solid right now."
The Mariners got their first three runs on homers off Chen -- Kyle Seager's solo shot to right field in the second and Casper Wells' two-run sock to left in the fourth. Their comeback culminated with Seager's RBI double over right fielder Jeff Francoeur's head in the seventh.
They were kept from going ahead in the eighth after Brendan Ryan tripled. Getz, playing in at second, grabbed Dustin Ackley's grounder and threw to catcher Pena, who put a fine diving tag on Ryan as his foot appeared to go over the plate instead of touching it.
"I didn't even know I went over it. It's just a weird thing," Ryan said. "I was going to try to get my foot in there and then maybe a hand, because the tag was coming down. It's a pretty tough call. That's crazy. That's the difference in the game."
The Mariners, despite being second-last in American League hitting and scoring, have come up with 25 runs and a .328 average in these three games against the Royals. And after losing the first two games of the series, this would have been a bitter loss for the Royals.
"There's no doubt -- putting up seven runs and getting a nice lead. You've got to give them credit for fighting back and not giving up," Butler said. "Hey, they brought their sticks this series, I'll tell you that. It's not all on our pitching staff -- heck, they might have been due as well. But that would have been a real tough one to drop."
Butler had a perfect night in the 103-degree heat with two singles, two walks and the game-ending 395-foot homer, just enough to reach the seats.
As Butler rounded third base, he tossed his batting helmet with glee.
"I had good distance on that, too," Butler said.