Indeed, just when Zack Greinke seemed to have a shutout within his grasp, Angels closer Ernesto Frieri dropped the ball. Or at least put it in the middle of the plate where the Royals could smash it.
Greinke got to within two outs of a 2-0 victory.
When Alex Gordon singled to left, Angels manager Mike Scioscia pulled Greinke and went with Frieri, also a right-hander. On the first pitch, Butler blasted a home run far over the center-field wall for a 2-2 tie.
Then, Perez belted a 1-1 liner high off the yellow foul pole in left for the Royals' sixth walk-off victory this season.
"It was really close. I started running and I saw the umpire put his hand up and I said, 'We got it!'" Perez said.
There was some planning that went into this back-to-back home run blitz. When Frieri trotted in from the bullpen, Butler and Perez got together near the Royals' dugout and recalled hitting coach Kevin Seitzer's advice: Watch for the fastball.
"I told Sal on deck, [Frieri's] predominantly [a fastball pitcher] and we've got to up there and not be late, and neither one of us were late," Butler said.
Frieri went with his heater and Greinke didn't blame him at all.
"It's part of baseball. Ernie's got a great fastball. Billy's a good fastball hitter," Greinke said. "He threw the best pitch to both those guys, and it just didn't work out. As a closer, you just do what you do."
Actually Butler was miffed because in the seventh inning against Greinke, he'd smashed a ball that seemed about to carry over the center-field wall, but Mike Trout settled under it for the catch.
"I was mad the whole time just waiting for my next opportunity to get up and do something, because I felt I put a pretty good swing on the ball and it didn't get out," Butler said. "I felt I had to redeem myself and it feels good when you do."
It felt about two runs and 423 feet worth of good.
"This park does funny things at night, but I knew that one was gone when I hit it," Butler said.
Up came Perez and, kaboom.
"Fastball, up and in. We were looking for the fastball from the closer," Perez said. "He throws a lot of heaters and that's what we were looking for."
Arcing through the night, the ball soon was bouncing off the foul pole -- after giving Yost and everyone else a flash of uncertainty.
"As it left his bat, I thought, 'All right, we've done it,'" Yost said. "Then it started slicing and I went from, yeah, to whoa, whoa, whoa."
It was the first walk-off home run of Perez's professional career and, according to veteran Jeff Francoeur, he made a first-timer's mistake by throwing his helmet straight up as he arrived at home plate. Frenchy was fearful the helmet might come down and bash a noggin or two.
"Not straight up?" Perez said, chortling. "I've got to throw it to Frenchy?"
It was a crazy finish to what unfolded as a taut pitching drama, as the matchup had promised with Greinke and Jeremy Guthrie on the mound. Here were two veteran right-handers obtained just before the Trade Deadline in July and both doing well for their new clubs.
Greinke, a Cy Young Award winner in his glory days for the Royals, had won his previous four starts for the Angels. Guthrie, who blossomed in Kansas City after being lost in the Colorado Rocky Mountains, had won four straight decisions for the Royals.
And both were again sharp and, as Guthrie so aptly put it: "It was fun."
Greinke gave up one run on five hits and two walks in 8 1/3 innings. Guthrie went eight innings, giving up two runs, five hits and one walk. Neither got a decision with Frieri taking the loss and Kelvin Herrera, after a scoreless ninth, getting the win.
In the first seven innings, the only run was Kendrys Morales' leadoff homer in the Angels' fifth inning -- his 20th of the season and his second in two games. Guthrie was doing some adjusting.
"For the most part, I made a lot of mistakes with my slider so I was forced to kind of pitch majority fastball, at least later in the counts," Guthrie said. "I tried to do the best I could to make good pitches and got ground balls most of the night. and we made good defensive plays."
The Angels scored their second run in the eighth on a dropped fly ball. Vernon Wells opened the inning with a single to right, but Guthrie got the next two batters on grounders, Wells moving to third. On a 3-2 pitch to Trout, Guthrie issued his only walk of the game.
Torii Hunter hit a line drive to right field but Francoeur squinted, ducked and failed to make the catch. Wells scored on what was ruled an RBI single.
"It went up in the lights and stayed there," Francoeur said. "I just turned my head and hoped it didn't hit me."
After tough losses to the Twins and the Angels in the previous two nights, this was a special kind of victory for the Royals.
"For me, in 7 1/2 years this is one of the most satisfying ones I've had," Francoeur said. "Because I believe this team can win games and we're better than what we're doing."