MINNEAPOLIS — The Minnesota Twins started this game sloppily and never recovered against the surging Kansas City Royals.

The biggest letdown of the afternoon came afterward, for Scott Diamond and Aaron Hicks.

Billy Butler had two hits and drove in two runs, Lorenzo Cain stole a home run from Trevor Plouffe with a leaping catch over the center field wall, and the Royals beat the Twins 7-2 on Thursday for their ninth straight victory.

Then the Twins sent starting pitcher Scott Diamond and center fielder Aaron Hicks to Triple-A Rochester. Corner outfielder Oswaldo Arcia will be recalled, and the Twins will make another move on Saturday to replace Diamond on the staff.

Diamond (5-10) was the only one in last year's rotation assured of a spot this season after going 12-9 with a 3.54 ERA in 27 starts. This year, his ERA is 5.52 and he has only 45 strikeouts in 107-plus innings. In his 20th outing, the Royals tagged him for seven runs, nine hits and three walks in five innings, rendering a homer and a double by Justin Morneau moot.

"If you're not impacting the team and contributing at all, you don't deserve to be here," Diamond said. "Right now I just need to go down to Triple-A and figure some things out and hopefully come back."

Diamond went 1-6 over his last 10 starts. Only two of those were turns of six innings or more and three runs or less.

"I just need to get back to being aggressive and clear my head and reset a little bit," Diamond said. "I think right now I'm trying to do a lot. I was fearful of this actually happening so I think because of it I was just trying to do too much."

Hicks, who made the opening day roster after never playing in Triple-A, has had quite a time adjusting to major league pitching. After a brief improvement right before the All-Star break, Hicks has regressed again. He's hitting .192 with 84 strikeouts in 281 at-bats. Even a rebuilding team with time to develop prospects couldn't let that continue.

"It looked like at one point he was going up the ladder a little bit, and now he's going right back down. A lot of poor at-bats. The kid's trying. He's playing a great center field. I'm happy with that, but unfortunately right now his swing is not where he wants to be. He needs some confidence too," manager Ron Gardenhire said.

Managing the strike zone is what Hicks needs to work on the most.

"This game is just a business. You have to be able to produce and produce on a daily basis. The past couple weeks I haven't really been producing that well," Hicks said.

Hicks said he'll try to take the positive out of his demotion.

"Just relax and be able to have fun playing the game and get that competitive edge back," he said.

Andrew Albers is the leading candidate to be summoned to replace Diamond. The left-hander is 11-5 with a 2.86 ERA in 22 starts for Rochester.

The Royals last won nine straight games when they opened the 2003 season at 9-0. The last time they won more in a row was a 10-game run in 1994, according to STATS research. The Twins were swept in a series for the eighth time this year.

James Shields (6-7) gave up two runs on five hits and five walks in six innings for the Royals, but against a team that hasn't hit for power, hasn't hit with runners in scoring position and hasn't been stealing bases, he was never really in trouble.

"That was an ugly series. Those guys came in here, wanted it more than us and found out ways to win games," Gardenhire said. "And we didn't. Striking out too many times. Missing too many opportunities."

In the field, too.

Plouffe misplayed at third a potential double-play ball to load the bases in the second inning, and Mike Moustakas and Justin Maxwell drove runs in to get the Royals on the board.

"Balls off the wall. Guys not going to pick it up. Standing there watching plays. Overthrowing cutoff men. Not acceptable," Gardenhire said.

The manager had a meeting after the game to address the lethargic performance with his players.

"I thought that was pretty ugly. Our fans don't deserve to watch that," Gardenhire said.

NOTES: Twins GM Terry Ryan said OF Josh Willingham (left knee) will leave for a rehab assignment with Triple-A Rochester this weekend. Willingham had surgery to repair a torn meniscus July 3 and said he hoped to be back with the Twins as soon as next weekend, when they have a series in Chicago against the White Sox. ... The Twins have three more games on this homestand, starting Friday with Houston. RHP Samuel Deduno (7-4, 3.18) will start the opener against the Astros, who have never been to Target Field.