Ryan Doumit threw wildly to second on a stolen base attempt, and the runner eventually scored.
Josh Willingham lost a fly ball in twilight, allowing two runs to score.
Darin Mastroianni tried to steal third -- with the Twins down four runs -- and was thrown out.
"Not a very good ballgame for us," Twins manager Ron Gardenhire said. "Some mistakes out there."
On this particular September night, this particular non-contender resembled a team that's counting down the days until the end of the season.
And Kansas City took advantage, rolling to a 9-1 victory while ripping eight extra-base hits around Target Field. Twins lefthander Scott Diamond (11-7) took the loss while Royals rookie lefthander Will Smith, (5-7) beat the Twins for the first time in three tries.
The Twins didn't pitch well, from Diamond not having his good control to Luis Perdomo hitting Lorenzo Cain in the helmet with a pitch in the eighth inning. Cain, by the way, stayed in the game and finished a homer run shy of the cycle.
Diamond gave up four runs over six innings on 10 hits and three walks with two strikeouts. He has a 6.64 ERA over his past four outings. After starting 6-1 at home, he's lost his past three decisions at Target Field.
"It seemed like I was up in the zone," Diamond said, "and that just might be from the adrenaline and getting back out there. I've got to continue to work down and in."
It wasn't all his fault, as many among the announced crowd of 28,993 were booing by the late innings.
Kansas City's Salvador Perez, an impressive young catcher, reached on a single in the second inning and took off for second when Diamond bounced a pitch to the backstop. Doumit got the ball and fired wildly to second, allowing Perez to move to third. He then scored on Jeff Francoeur's single for the first run of the game.
The inning was just starting. Eric Hosmer singled to put two runners on. Diamond struck out Johnny Giavotella for the second out, then got Cain to hit a routine fly ball to left -- or it should have been.
Willingham immediately flashed the international signal for "I lost the ball'' and the ball fell about 20 feet behind him as two runs scored to make it 3-0.
Ah, Metrodome memories.
"Just the time of day," Willingham said. "It had nothing to do with the lights."
And the Twins were inefficient on offense, going 1-for-9 with runners in scoring position. Baserunners were thrown out twice by Perez, once in the first inning when he gunned down Jamey Carroll during a double steal, and then Darin Mastroianni in the fifth when he took off for third with no outs, runners on first and second and the Twins down 4-0.
"Some base running was not very good," Gardenhire said. "Trying to be aggressive, but you know, you've gotta make sure in those situations, we can't get thrown out in those situations, we've got some big guys at the plate.
"So not a very good ballgame. We went from really good [Monday] to not very good [Tuesday], but you also have to credit the other side."
If anyone is wondering, there's 20 games to go.