The skidding Chicago White Sox traded closer Michael Kopech to the Los Angeles Dodgers on Monday as part of a three-team deal that also sent right-hander Erick Fedde and outfielder Tommy Pham to the St. Louis Cardinals.

The White Sox unquestionably are sellers. They are long out of postseason contention and losers of a single-season, franchise-worst 15 straight games entering Tuesday’s visit from the Kansas City Royals.

Kansas City, meanwhile, is sticking around a tight American League wild-card race and remains sold on closer James McArthur, who shook recent woes by saving Monday’s come-from-behind 8-5 victory in the series opener.

“Luckily for me, we have a really good pitching department here,” McArthur said, “and those guys have been working with me through this whole thing, and they work with me whenever things are going good, too.”

McArthur pitched a perfect ninth Monday to pick up his 18th save. He suffered a blown save against Arizona — his fifth this season — on Wednesday. He entered Sunday’s game against the Chicago Cubs with the Royals trailing 4-3 but allowed three runs as the visitors put things out of reach.

Kansas City rebounded one day later, using a six-run eighth inning outburst to surge past the White Sox. Bobby Witt Jr. went 4-for-5 and belted a go-ahead grand slam on the first pitch he saw from John Brebbia.

“Sometimes, we don’t give the bullpen enough room for mistakes,” White Sox manager Pedro Grifol said. “Today, we had a three-run lead. I felt our two best guys (Steven Wilson and Brebbia) were on the mound.”

In four games against the White Sox since the All-Star break, Witt Jr. is hitting .812 (13-for-16) with two home runs and seven RBIs.

He’s batting .545 during an 11-game hitting streak and credits keeping an even keel.

“Just control what I can control in the box. Look for a pitch I can hit and then just take my swing that I prepared for before the game and see what happens,” Witt Jr. said

Losers of 14 straight from May 22 to June 6, the White Sox appeared primed to stop their latest skid on Monday. Behind six strong innings from Chris Flexen, three hits from Luis Robert Jr. and an Andrew Vaughn solo home run, the White Sox led 5-2 after seven innings.

Kansas City’s Michael Wacha (7-6, 3.65 ERA) is set to oppose Chicago’s Jonathan Cannon (1-5, 4.43) in a matchup of right-handers.

Wacha was the winning pitcher on July 19 when the host Royals beat the White Sox 7-1. He pitched seven shutout innings.

Wacha is 4-1 with a 3.30 ERA in eight career starts against the White Sox, including a 2-1 mark in three starts this season.

A rookie, Cannon faced the Royals in his major league debut on April 17 and again on July 20, when he allowed four runs and eight hits in six innings of a road defeat. He is 0-1 with a 4.09 ERA in two starts versus Kansas City.

Cannon has lost three straight starts. On Thursday, he scattered two runs and eight hits in six innings in a 2-1 loss at Texas.