Diamond, though, was hurt by several ground balls and bloop hits and said he suffered from some bad luck in his outing. But it still led to him giving up four runs on a season-high 10 hits and two walks over six innings.
"I really don't second-guess any of the pitches I threw tonight," said Diamond, who fell to 8-4 with a 3.16 ERA. "I felt like I executed well. It was just frustrating the way the results happened. It seems like there were a lot of groundballs that just found their way. Same thing with the bloops. But it's just the way it goes sometime."
Twins manager Ron Gardenhire agreed and added it brought back memories of when his team played in a similar fashion before moving to Target Field.
"It honestly reminded me of the Metrodome days, when we had those guys who could chop the ball and slap the ball, and roll them through and find holes," Gardenhire said. "So the Royals did a super job. They were very aggressive on the basepaths. They were chopping the ball all around."
The Royals struck early, scoring in the first inning on an RBI single from Lorenzo Cain with two outs. They tacked on another run in the second, when Yuniesky Betancourt singled to bring home Mike Moustakas.
The Twins tied it up in the fourth on a pair of RBI groundouts from Joe Mauer and Chris Parmelee against Royals starter Luis Mendoza.
But Kansas City regained the lead with two runs in the fifth against Diamond. Cain brought home the first with an RBI single before Parmelee made an error at first base with the bases loaded that allowed a run to score.
"We watched a lot of film on him," Royals left fielder Alex Gordon said of Diamond. "We didn't want to do too much, but I think that's what we did. We didn't really have any home runs or many doubles or anything like that, but just a lot of singles and good at-bats that we put together, and we were able to chip away."
Minnesota pulled within one run in the seventh, as Jamey Carroll doubled to score Parmelee. But the Twins failed to capitalize with runners at second and third with one out against reliever Jose Mijares, as Denard Span grounded into a fielder's choice and Ben Revere flied out to left to end the inning.
The Royals added an insurance run in the bottom half of the inning against reliever Jeff Gray, with Cain lacing an RBI double off the wall in left field for his third run-producing hit.
Kansas City capped the scoring with two in the eighth on RBI hits by Betancourt and Gordon.
Mendoza also did his part to hold the Twins' offense in check. The right-hander went 6 1/3 innings, allowing three runs on seven hits with two walks and four strikeouts to earn his first win at home this season.
Mendoza's last victory also came against the Twins on June 29 at Target Field.
"They played good baseball tonight," said Span, who left the game in the eighth inning because he was feeling dizzy. "They came out in the first inning and set the tone. Mendoza pitched good. It was the second time in a row he pitched well against us. And they had some hits that found holes and had eyes. They caught some breaks today, but they were also aggressive."