The left-hander gave up just two runs on six hits over eight strong innings to improve to 7-3 with a 2.63 ERA in 11 starts on the year.
"I'm just trying to focus on strike one," said Diamond about the key to his success. "The rhythm's going pretty good. But right now, I'm just trying to throw strikes and keep the game going. And get us right back in there so we can keep hitting."
It was a solid outing by Diamond, which was even more magnified because it gave the bullpen much-needed rest heading into Saturday night's game with rookie right-hander Cole De Vries getting the start.
"I was impressed by the fact he was keeping the baseball down and he was mixing up his pitches," Royals catcher Brayan Pena said. "He gave them a lot of innings, especially with his doubleheader, so he did a good job."
Diamond was backed by a strong showing by the offense, which scored more than five runs for the first time since June 13.
Sanchez struggled all afternoon, as the left-hander allowed 10 hits and walked six more in just 4 1/3 innings.
The Twins stranded several runners early in the game, but finally came through with two runs in the third on an RBI double from Trevor Plouffe and a sacrifice fly from Ryan Doumit.
"There were a lot of guys left on base in the first three innings and you always wonder if that's going to come back and bite you," Twins manager Ron Gardenhire said. "But, fortunately, we put together an inning and Diamond shut them down."
That big inning came in the fifth, when the Twins scored four runs off Sanchez. They scored the first run of the inning on an unusual RBI single from Brian Dozier with runners on first and second. Dozier hit a ball that started foul behind the plate, but spun fair, which allowed Dozier to reach first on an infield single and Doumit to score from second because no one was covering home.
"That's what I was trying to do," Dozier said with a laugh. "No, it's just one of those things. I think that's the first time I've actually seen it come back. A lot of time you'll see it spin and spin, everybody's waiting on it. But yeah, I saw it on film, it actually hit behind the batter's box."
Gardenhire was equally amazed by the play, as they ended up giving the scuffed-up ball to Dozier as a souvenir.
"Never seen one spin like that," Gardenhire said. "That ball came from behind the batter's box. ... We kept the ball. Ripley's Believe It or Not or something. Or Guinness Book of Records for farthest foul ball that ever went fair."
After a double-steal, Alexi Casilla came through with a two-run double and eventually scored on a single from Denard Span that knocked Sanchez out of the game.
Plouffe put the icing on the cake with a solo homer in the eighth. It was his 16th of the season and his 11th this month.
Kansas City didn't score until the sixth, as Jason Bourgeois led off the frame with a single, advanced to second on a wild pitch and scored on a Yuniesky Betancourt groundout.
The Royals scored again in the eighth on an RBI single from Betancourt with one out. But Diamond was able to strand runners at second and third by striking out Mike Moustakas and Billy Butler to end the inning.
Diamond gave a fist pump after striking out Butler and said it was partly because he got out of the jam and partly because he struck him out on a hanging curveball.
"It was probably a combo," Diamond said. "I got out of the inning, but definitely because he's a great hitter and I got away with one. That's for sure."