He came through again in the clutch Sunday.
With one run already across in the sixth, Willingham hit a three-run homer to tie it at 5. Two batters later, Plouffe hit a solo shot for his second of the day.
Willingham, who signed a three-year deal in December to basically replace Michael Cuddyer at a lower price, has 17 home runs and a team-leading 55 RBIs.
"The only thing I can say is I'm happy with the way my season's gone so far. Obviously, we want to keep winning as a team," he said. "(Joe's) going to represent this team well."
Others in the clubhouse were more forthright in their disappointment.
"He's been there from Day One, he's been carrying the load for our baseball team an awful lot," manager Ron Gardenhire said. "I sure was hoping he would get a chance to play in an All-Star game. He's very deserving of it and he just added onto his numbers today."
Said Plouffe: "Joe is obviously having a great year and deserves it, and I think Josh deserves it just as much. I'm not happy to see that he didn't make it because I think he's been carrying our team all year."
Plouffe also hit a solo homer in the second inning. Butera added a three-run shot in the eighth for a 10-5 lead.
"I don't get tired of seeing three or four home runs a game, especially if it's our team," Gardenhire said.
The first three Minnesota home runs came off Bruce Chen (7-7), who had mostly breezed through the first five innings.
Chen, who had allowed just one earned run in each of his last two starts, gave up six earned runs and six hits in 5 2/3 innings. Irving Falu drove in four runs for the Royals.
Reliever Jeff Gray (4-0) got the last two outs of the sixth and the first of the seventh for Minnesota.
Brian Dozier led off the Twins' sixth with his first career triple and scored on a squeeze bunt by Denard Span. Jamey Carroll walked and Mauer singled up the middle before Willingham hit a 416-foot home run, his 17th of the season.
Plouffe's second home run was his 18th of the season. Thirteen of them have come since June 1.
"I'm not trying to hit home runs. I can tell you that much," he said.
Span added an RBI single in the seventh.
Twins starter Francisco Liriano gave up five runs -- four earned -- in 5 1/3 innings.
Liriano said he's been more relaxed since rejoining the rotation in late May, which has led to greater confidence. He was that way early, cruising through three innings but danced with danger the next three.
The left-hander gave up a single to Billy Butler leading off the fourth and walked Yuniesky Betancourt two batters later, prompting a mound visit from Butera. After a single by Eric Hosmer loaded the bases, a sacrifice fly by Brayan Pena tied it at 1. But Jason Bourgeois struck out to end the threat.
A double play helped Liriano escape a fifth-inning jam, but he didn't get that in the sixth.
Betancourt singled with one out and Hosmer was hit by a pitch, before a batted ball by Pena deflected off Liriano for an infield single to load the bases. A single by Bourgeois off the glove of first baseman Justin Morneau scored two -- the latter on an error by right fielder Darin Mastroianni who overran the ball.
Liriano was replaced by Gray, who promptly gave up a two-run double to Falu to make it 5-1.
"It's just one of those days," Kansas City manager Ned Yost said.
Pena added an RBI single and Falu a two-run single in the ninth against Glen Perkins.
Butler, the Royals' All-Star, was 1 for 4, including a strikeout with two runners on in the eighth inning.
"It's a good feeling," he said of his selection. "It's just tough when you have a game like that, it puts a damper on things. It's an honor to do it, especially when we're hosting it, so I get to do it in front of my hometown fans."
Royals closer Jonathan Broxton is one of the final five candidates to be voted into the All-Star game by fans. Voting ends Thursday. ... Falu singled in the fifth to end an 0-for-17 stretch. ... Kansas City continues its 11-game, 10-day road trip Monday in Toronto with Everett Teaford (0-1, 5.06) scheduled to face Ricky Romero (8-2, 4.94). ... Minnesota starts Liam Hendriks (0-5, 6.82) on Monday in the first game of a four-game series in Detroit. He'll face Doug Fister (1-5, 3.91). ... The game was the Ninth Annual Armed Forces Appreciation Day, as the Twins organization honored veterans and active service members.