Neftali Feliz, who saved 72 games in the Rangers' back-to-back World Series years, was called on to record the final out of the eighth inning with the bases loaded and Alcides Escobar at the plate.
And he walked him on four pitches, giving the Royals a 2-1 lead that Kansas City closer Greg Holland would not relinquish.
Jason Frasor, who took the loss, started the eighth for Texas, and struck out the first two Royals he faced. But two singles and a walk loaded the bases before Ron Washington called for Feliz from the bullpen.
Feliz exited after the bases-loaded walk, and Joe Ortiz recorded the final out of the eighth.
Rangers' starter Martin Perez and Royals' starter Ervin Santana each allowed one run in their respective starts. Perez threw five and two-thirds innings, while Santana took a low pitch count into the eighth inning.
The teams exchanged runs in the second inning.
In the top half, A.J. Pierzynski smoked a 0-1 pitch off the right-center field wall for a no-out, RBI double. Adrian Beltre scored, aided by an errant relay throw from Emilio Bonifacio.
The Ranger second ended with Pierzynski standing on second base.
The Royals scratched out a run in the second on a Justin Maxwell RBI double. Maxwell hit a sinking line drive to center field that fell just shy of the glove of a sliding Leonys Martin.
Maxwell was stranded at second as well.
And that's all the scoring either team managed until the bottom of the eighth inning. The Royals left 11 men on base, including runners in scoring position in the fourth through the sixth innings.
Elvis Andrus struck out with the bases loaded to end the top of the fifth inning, stranding three Rangers.
Perez was drilled by a Billy Butler line drive in the bottom of the fifth inning, but won the third Battle of Men Named Perez, as Kansas City's Salvador Perez lofted a broken-bat liner to Beltre at third, stranding two Royals to end the inning.
Santana threw less than 10 pitches in four different innings the first, third, sixth and seventh innings as the Rangers recorded only five hits off of their former division counterpart.
Santana threw 94 pitches in his 7.1 innings, while Perez tossed 108 in less than six innings for Texas.
Neal Cotts relieved Perez in the sixth inning, and pitched through the seventh inning without surrendering a hit.
The loss drops Texas out of the top two wild card spots, as Cleveland won in a rain-shortened game against the Astros earlier Friday.
So, yes, if the season ended after Friday's game, the Rangers would be out of the playoff picture. The Royals moved to within two games of the Rangers in the Wild Card standings.
The Rangers and Royals continue a three-game set in Kansas City Saturday night. First pitch is scheduled for 6:10 p.m. CT.