KANSAS CITY, Mo. — This first one will sting.

In the first game of a doubleheader on Sunday, the Royals lost 8-7 to the Seattle Mariners. The final score only told half the story.

On an afternoon at Kauffman Stadium, the Royals partially gifted their opponent a 7-0 lead. They clawed back over the final seven innings, slicing the deficit to 8-7 on a two-run homer by Mike Moustakas in the eighth. In the end, they were doomed by a calamitous sequence in the top of the second inning, a mediocre start by Danny Duffy, and two home runs by Mariners slugger Nelson Cruz.

Duffy surrendered seven runs (three earned) in 5.2 innings. He allowed two homers in the top of the first. The difference in the ballgame stemmed from four unearned runs yielded in the top of the second.

“It’s just an interesting, really unprecedented turn of events that you don’t really see jumble all together that often,” Duffy said.

The sequence included the following:

Duffy issued a walk to shortstop Jean Segura with two outs after just missing on a 3-2 pitch near the bottom corner of the strike zone. The pitch was borderline. Duffy saw it “as a strike,” he said. He did not get the call from home-plate umpire David Rackley.

“You can’t miss that pitch,” Duffy said, “especially when it’s to a hitter the caliber of Segura.”

Moments later, Duffy picked Segura off first base, only to watch him scramble back safely to the bag. The breakdown was two-fold. First baseman Eric Hosmer started to chase after Segura before firing a throw to second base.

Duffy was late to first base to join the rundown, and Hosmer found himself out of position, catching the return throw from second in the baseline as Segura zoomed back into first.

“It was a play where we needed to run ’em down just a little bit more,” Royals manager Ned Yost said. “And Duff was a little late getting there.”

Duffy still nearly escaped the inning with zero damage done. On an 0-2 pitch to Robinson Cano, Duffy threw a 94-mph fastball that tailed inside. Cano swung and missed for strike three. But catcher Drew Butera, set up on the outside corner, lunged back across the plate and could not catch the ball. It kicked away, bouncing off the leg of the umpire.

Segura scored from second as Butera jogged somewhat casually after the ball and Duffy was slow to cover home plate. The play would eventually be ruled a passed ball, meaning all runs were unearned.

“He didn’t know if it hit off Cano,” Yost said of Butera. “There was just some indecision on his part. We were screaming home, home, home. He wasn’t sure, because he was sitting so far outside.”

With the deficit still just 4-0, Duffy worked ahead 1-2 in the count against Cruz. Moments later, Duffy threw an 82-mph change-up that stayed up. Cruz crushed a three-run shot to left field.

In seconds, the inning had turned disastrous. A borderline ball four. A botched rundown. A passed ball that made all four runs unearned. A 7-0 deficit after two innings.

The Royals pecked away at the lead, scoring two times in the third on a homer by Whit Merrifield and three times in the fifth. Cruz stretched the Mariners’ lead back to 8-5 with a homer against Scott Alexander in the seventh. But Moustakas clubbed a two-run homer to right field off Mariners reliever Nick Vincent in the eighth ... before the Royals put the tying run on second base with one out.

Alex Gordon and pinch hitter Brandon Moss couldn’t come through in the eighth. One inning later, the Royals put a man on base with two outs, but Seattle closer Edwin Diaz retired Melky Cabrera on a fly ball to left field, closing out the game.

“The (second) home run that Cruz hit,” Yost said, “was the one ended up breaking our back right there.”