Leaky bullpen costs Kansas City Royals in Wednesday night’s loss to Seattle Mariners

An ineffective bullpen cost the Kansas City Royals dearly in a 6-5 loss to the Seattle Mariners on Wednesday night at Kauffman Stadium.

Royals reliever James McArthur operated as an opener and surrendered three runs in his lone inning. Mariners outfielder Julio Rodriguez hit a leadoff double and catcher Cal Raleigh hit a two-run homer.

The Royals allowed six walks in the game. Rookie pitcher Alec Marsh surrendered four hits, one run and five walks. He also struck out six as KC’s “bulk” reliever.

“You aren’t going to have your best stuff all the time, but you’ve got to find a way to get it done,” Marsh said. “The command of the slider wasn’t great. ... At the end of the day, I thought the biggest positive was coming out of that game and giving us a chance to come back.”

The Royals tried to overcome their inefficient pitching by scoring some early runs against Mariners starter Luis Castillo. Royals third baseman Maikel Garcia, who extended his hitting streak to 18 games, doubled in the first inning and later scored on a sacrifice fly.

Royals outfielders MJ Melendez and Kyle Isbel each recorded RBIs as well.

Castillo earned a no-decision. He allowed nine hits, four runs and struck out three.

“They had good at-bats from the get-go and I was really pleased with it,” Royals manager Matt Quatraro said. “We weren’t able to put up a big number to take the lead, but overall, they did a good job battling.”

In the eighth inning, Mariners outfielder Teoscar Hernandez hit a go-ahead sacrifice fly to break a 4-4 tie. Rodriguez added another run in the ninth.

It would be a pivotal run.

“We have to figure out a way to put up zeroes,” Quatraro said. “You come into close games and that’s your job, to keep it where it is. We had better luck some nights than others. But that is the end goal for all these guys.”

Royals outfielder Nelson Velázquez hit a solo homer in the ninth, his sixth of the season and his third since joining the Royals. However, Mariners closer Matt Brash rebounded to earn his third save.

The Royals dropped to 39-83.

Missed previous games of the series?

Game 1: Dairon Blanco’s sacrifice bunt lifts Royals over Mariners

Game 2: Bobby Witt Jr. hits grand slam as Royals fall 10-8 in extra innings

Here are more notables from Wednesday’s game:

Melendez doubles, Salvy shows wheels in 3rd

The Royals got early run production from the middle of their lineup. In the third inning, Melendez hit an RBI double that scored catcher Salvador Perez.

Perez raced around the bases to score from first base. The Royals pulled within a run as Perez slid across home plate.

“Just trying to put the ball in play has been the biggest thing for me,” Melendez said. “I’m really not trying to do too much and definitely being OK with singles.”

Melendez recorded his 23rd double of the season. He finished 3 for 3 and turned in his second consecutive three-hit night. Melendez has collected multiple three-hit nights in his last nine games.

Perez has scored 47 runs this season.

“It’s always awesome,” Melendez said of watching Perez run the bases. “I think that’s like the third time that I’ve personally been hitting and he scored from first base. ... He’s definitely got some wheels and it’s pretty awesome to see him making that hustle play.”

Roster moves: Royals call up Double-A reliever

The Royals promoted reliever John McMillon from Double-A Northwest Arkansas.

McMillon made 37 appearances across three minor-league levels. He also pitched in Low-A Columbia and High-A Quad Cities. He went 7-3 with a 2.10 ERA and 10 saves in the minors.

He was electric in Double-A, as well. McMillon allowed two runs in 20 2/3 innings and struck out 30 batters. The right-hander is set to be the fifth Royals prospect to make his MLB debut this season.

“The first person I called was my mom,” McMillon said. “We’ve been praying about this for a long time. So I was really glad to give her some good news.”

McMillon is the No. 25 prospect in the Royals’ farm system. He excels with an upper-90s fastball and solid slider. Strikeouts are McMillon’s calling card: he registered a 23.5% swinging-strike rate in late July.

In a corresponding move, the Royals optioned reliever Nick Wittgren to Triple-A Omaha and transferred starting pitcher Brad Keller to the 60-day injured list. Wittgren elected to become a free agent.

The Royals’ major-league reserve list (commonly known as the 40-man roster) now sits at 39 players.

What’s next: The Royals finish their four-game home series against the Mariners on Thursday. Angel Zerpa will be KC’s starting pitcher.