Alex Gordon added a two-run homer for the Royals, who won three of the four games in this series. Billy Butler went 5-for-5 with an RBI and a run scored and Emilio Bonifacio went 4-for-6 with two runs.
Kansas City starter Jeremy Guthrie allowed five runs on seven hits over six innings. Louis Coleman (3-0) recorded the final out in the top of the 13th to pick up the win.
Justin Smoak and Raul Ibanez homered for the Mariners, who have lost four of five. Kendrys Morales and Brad Miller each knocked in a run.
Joe Saunders got the start for Seattle and gave up three runs on 11 hits over 4 2/3 innings. Chance Ruffin (0-1) took the loss after giving up the homer to Moustakas.
"I love those situations," said Ruffin, who had not pitched in the majors since 2011. "I just made a mistake."
The Mariners scored five runs over the first four innings, with three of those runs coming in the first. Abraham Almonte doubled to right and scored on Morales' single to center. Smoak followed with a homer to right.
Seattle tacked on another run in the third. Kyle Seager and Morales hit consecutive singles with one out. Smoak then flied out to right, but first baseman Eric Hosmer's error allowed a run to score.
In the fourth, Miller's sacrifice fly made it 5-0. Michael Saunders led off with a double to left-center field, moved to third on Henry Blanco's groundout and scored when Miller flied out to left.
"It's not easy to come back from a five-run deficit," Butler said. "That shows the resiliency of this team."
Kansas City started its comeback with three runs in the fifth. Jamey Carroll doubled to left and crossed the plate on Gordon's homer to right. Bonifacio and Butler singled to put men on the corners with two outs. Salvador Perez followed with an RBI single to left.
The Royals scored three more runs in the seventh. Bonifacio led off with a single and raced home on Hosmer's double off the wall in center. Hosmer scored on Butler's single to right. Brett Hayes doubled to put men on second and third. Charlie Furbush came in from the bullpen and gave up a sacrifice fly to Justin Maxwell, which made it 6-5 Kansas City.
Ibanez came on as a pinch-hitter with two outs in the ninth. He smacked Greg Holland's 3-2 pitch over the wall in right to tie the game.
Perez went 3-for-3 before leaving the game due to mild dizziness ... The Royals had 19 hits, compared to 11 for the Mariners ... Kansas City went 3- for-13 with runners in scoring position and stranded 11, while Seattle went 1- for-10 with RISP and left eight men on ... The Mariners pushed back Felix Hernandez's start from Sunday to Wednesday, after he left his Monday start against the Royals with lower back cramps.
09/05 21:00:41 ET