One inning showed the difference between the Royals and Cubs — and why one team is gearing for a postseason push and another is trying to salvage a difficult season.

The Cubs stranded runners on second and third with no outs in the top half of the 5th and then in the bottom half, the Royals put up a crooked number — thanks to a misplay in the field — after having no runners on base in the frame with 2 outs, as Kansas City took the series open at Kauffman Stadium, 6-0.

With runners on second and third and 2 outs in the bottom of the 5th, Kyle Hendricks looked to have picked up an inning-ending flyball to right field.

But Seiya Suzuki took a couple of steps backwards instead of in and that would be enough to cost him — he slid but could not make a play on the ball, leading to 2 runs and extending an inning in which the Royals would score all 6 runs.

“In terms of today, I feel like that fly ball in the 5th, if I caught that, the home run wouldn’t have happened and we would have built momentum into the next inning,” Suzuki said after the game through interpreter Edwin Stanberry. “I think reflecting back, I should have caught that fly ball.”

In an old-fashioned pitcher’s duel, Hendricks and Brady Singer were keeping both offenses at bay through 4 innings.

Then, in the top of the 5th, Mike Tauchman was hit by a pitch to lead off the inning and Dansby Swanson hit a looping single to left-center that advanced Tauchman to third and moved Swanson to second.

That’s the exact type of situation the Cubs have struggled in all season. Entering Friday, the Cubs were second-worst in batting average with runners in scoring position — .221.

Miles Mastrobuoni hit a ground ball to second base while the Royals’ defense was playing medium deep, preventing Tauchman from going home and picking up the first out of the frame. Then Miguel Amaya hit a shallow fly ball to center field and the Cubs tested Kyle Isbel. Isbel responded by nabbing Tauchman at the plate to kill the rally — their woes in clutch situations continuing.

Then the Royals made the Cubs pay, putting up the crooked number in the bottom half of the frame — like they have all season. They had the best batting average with runners in scoring position (.292) entering Friday and thrived again, thanks to Suzuki’s mistake.

“He moved back at first and that was enough to let it fall in,” manager Craig Counsell said after the game.

The Royals continued to make the Cubs pay. They hit two more singles to make it 3-0 and then Salvador Pérez put the exclamation point with a 3-run home run.