"We still like Nate and what he brings to the table," Servais said. "He's an asset, and we need to put him in the best spot to help us right now."
Miley and Taijuan Walker will rejoin the rotation this week, with Miley facing the Pirates on Wednesday now that his sore left shoulder has healed and Walker starting the opener of a four-game series against the Orioles after skipping his last start to rest a sore arch in his right foot.
LeBlanc, 31, appears to have a place for now in the rotation after throwing six scoreless innings on Friday against the Cardinals in his first Major League start since 2014. He'll start again Friday against the Orioles.
That means Karns shifts to the bullpen in a move Servais declined to call permanent, but clearly will be for the near future at least.
"Our club certainly welcomes the arm down there," Servais said. "But more importantly, give him a breather, get him back on track and try to get him in a good spot. It wasn't an easy decision. He was probably one of our more-consistent starters for a six- or seven-game stretch there. It hasn't been there the last four or five times out."
Servais is hoping Karns might excel in a relief role in the same way lefty Mike Montgomery jumped on his opportunity when moved to the 'pen in the spring.
"He's certainly got the stuff to do it, there is no question about that," Servais said. "We'll pick our spots, maybe similar to what we did with Montgomery earlier in the year. He can certainly take multiple innings. He's got all that in his bag. It's a different mentality, a little less thinking and just trust your stuff and go right after them. You never know. His stuff might tick up. It certainly did with Montgomery."
• Lefty reliever Charlie Furbush threw a 35-pitch bullpen session Tuesday and will advance to live batting practice on Saturday as he works back from his lengthy battle with shoulder issues.
"I'm not throwing 120 percent, but it's 90-95 percent," he said. "I'm ready to get on the mound and see what I've got."
• Three more Draft pick signings were announced by the Mariners -- 15th-rounder Danny Garcia, a left-hander from the University of Miami; 19th-rounder DeAires Moses, a center fielder from Volunteer State CC in Tennessee; and 34th-rounder David Ellingston, a right-hander from Georgetown. The Mariners have now signed 25 of their 40 picks, including 17 of the top 20.
• Left fielder Norichika Aoki went 2-for-4 with a walk and an RBI in his debut for Triple-A Tacoma on Monday in a 6-2 victory at Fresno. Catcher Jesus Sucre also made his first appearance for the Rainiers, going 0-for-3 as he returns from a broken leg suffered during winter ball in Venezuela on Jan. 17.
• Nick Neidert, last year's Mariners top Draft pick (60th overall), allowed three hits and two runs over seven innings in Class A Clinton's 5-3 victory at Wisconsin on Tuesday, improving to 5-1 with a 2.21 ERA.