"I know [the Royals] like their bullpen," said manager Terry Francona. "I can see why."
The loss, coupled with a Yankees win, closed Boston's divisional lead against its archrival to an even seven games.
Julian Tavarez started strong but faded quickly in innings four and five. The culprit? He shied away from the inside corner, lobbing too many changeups and sliders down the middle and not enough sinking fastballs, his bread-and-butter during a promising June.
"You can't make mistakes in this game, especially at this level," Tavarez said. "Today I made a lot of mistakes. I wasn't able to be consistent with a game plan."
Kansas City's Billy Butler delivered the decisive blow with his fifth-inning double into the left-center-field gap, which turned a one-run Boston lead into a 5-4 Royals advantage. Alex Gordon took care of the rest, knocking Tavarez out of the game by singling in Butler.
With Tavarez closing in on his highest single-season inning total since 2002, his performance has declined. Five straight starts have resulted in losses. The Red Sox went 6-1 in his previous seven.
But he insists that fatigue is not a factor.
"I can't say that I'm tired, because I'm not," he said. "When I want to hit 93 [mph], 92, I can hit it. I blame myself.
"That's how it goes," he added, "you know what I mean? I wish I could take it back and start over again, but you can't do that in this game."
The Sox touched up Perez during a four-run fourth, with Lugo delivering a bases-loaded blow to the Kansas City lead. Lugo smashed the first pitch he saw for a double down the line. Two runners scored, but Crisp held at third, only to scamper home safely after J.D. Drew's hot liner to left became a sacrifice fly on a diving catch.
"We scored four," Francona said. "You want that shutdown inning so bad, and they come back and score four."
Once again, the Kansas City 'pen strung up a series of zeroes. Then, in the bottom of the eighth, with the Royals up, 6-5, Crisp launched a rocket off Joakim Soria toward the right-field fence.
He thought it was a homer. At Fenway Park it landed for a triple.
"It is what it is when you're playing here," Crisp said.
"If it's not 380 in right-center," added Mike Lowell, "this game's tied."
There were two outs. Lugo, who stepped to the plate on a 15-for-29 tear, popped up on a Soria fastball.
"Outside corner," Lugo said. "I just couldn't get good wood on it."
The Sox managed only a David Ortiz single in the ninth off Kansas City closer Octavio Dotel. Manny Ramirez popped out to end the game.
"You can't win them all," Crisp said. "But we've been doing a good job of trying."