Plouffe and Willingham have gone yard in the same game five times since June 4, regularly exchanging the team's home run lead.
"I think it's just coincidence," Plouffe said. "I've definitely learned a lot from him this year. Just about what kind of hitter I want to be and staying within myself -- not trying to do the things I can't do. It's worked out. We're both putting some balls in the seats lately and that's helping the team."
Seventeen of Plouffe's 18 homers have come in his last 37 games, dating to May 16.
"[Plouffe's] just been going along unbelievable," Twins manager Ron Gardenhire said. "It's huge for us. He's taken over at third base where we were having some issues and putting a lot of balls in the seats. He's got kind of that natural swing, I guess. He just takes a smooth swing and the ball goes flying."
Besides a solo home run from Plouffe in the second, the Twins struggled to hit opposing starter Bruce Chen early and scraped together only two hits through five innings. Then they teed off in the sixth.
Brian Dozier scored on Denard Span's sacrifice bunt after Dozier led off with a triple. Chen walked Jamey Carroll and allowed a Joe Mauer single before Willingham connected for a three-run shot. Plouffe followed two batters later with his second home run of the game.
"We got down early and Chen was kind of rolling," Willingham said. "We got an opportunity there in the sixth and took advantage of it."
Span drove in Dozier again in the seventh with an RBI single. Then Butera's homer extended the lead to 10-5 in the eighth.
"Butera's homer ended up killing us, but our guys just stayed after it, they didn't quit and I'm proud of them for that," Kansas City manager Ned Yost said. "They made it interesting till the end."
Glen Perkins allowed a brief rally in the ninth. He retired the Royals' first two batters, but Kansas City strung together four straight hits and scored three runs before Alex Gordon grounded into a fielder's choice.
"Perk had his rough time out there," Gardenhire said. "Too many fastballs over the middle of the plate, he kept pumping them in there. You have to mix it up. It got exciting at the end, but a very nice win."
Francisco Liriano struggled to command the ball for most of his start, and he finally gave way to a Royals rally in the sixth. He loaded the bases with one out after giving up singles to Yuniesky Betancourt and Brayan Pena and hitting Eric Hosmer. Jason Bourgeois hit a ball off of Justin Morneau's glove for an error. Darin Mastroianni was also charged with an error as he misplayed the ball in right, allowing Betancourt and Hosmer to score.
With Liriano at 107 pitches, Minnesota turned to Jeff Gray (4-0) from the bullpen. But Irving Falu lined a two-run double on Gray's third pitch to give Kansas City a 5-1 lead. Gray walked Gordon before ending the inning with two groundouts.
Liriano's start was his shortest since he rejoined the Twins' rotation on May 30. He gave up four earned runs on five hits and four walks after posting a 2.41 ERA in his previous six outings.
"One of those games where I didn't have my best stuff," Liriano said. "It was one of those games you have to battle through. You don't have your best location with the fastball."
Kansas City scored its first run on a sacrifice fly in the fourth. Liriano stranded runners on second and third to end the inning.
Mauer's sixth-inning single extended his hitting streak to nine games, his longest since a 15-game streak Aug. 2-18, 2009.