James Paxton isn’t done staking his claim to a rotation spot for the start of next season.

On a day the Mariners announced that top mound prospect Danny Hultzen has potentially serious shoulder damage Paxton fanned 10 hitters in dealing a major blow to the Kansas City Royals’ playoff hopes. Paxton blanked the Royals on four hits over seven innings Tuesday night in a 4-0 win that leaves Kansas City just a game away from elimination.

Paxton didn’t walk anyone in his 97-pitch outing and became the first Mariners rookie to record double-digit strikeouts since Hisashi Iwakuma had 13 against Toronto last year.

“It could just be the electricity and being out there’’ Paxton said of his success going 3-0 with a 1.50 earned-run average in four big league outings after a so-so Class AAA season. “It kind of just raises your intensity up that much more. I think it just helps me get more locked in.’’

Justin Smoak then took Bruce Chen deep to left in the fifth inning for a three-run homer that gave Seattle a 4-0 lead and Paxton all the offensive support he’d need. It was Smoak’s second home run in three days batting right-handed and only his second all year from that side compared to 17 batting left-handed.

“I’m just trying to keep my bat in the zone longer’’ Smoak said of his right-handed hitting. “I feel like I’ve been letting the ball travel a little bit better. I’m having a little bit better at-bats and it’s starting to show a little bit.’’