Manager Scott Servais said it was disappointing that Karns wasn't able to get back on track.
"It was a struggle for Nate tonight to get much going," Servais said. "Location wasn't great, sequences weren't great. We were fortunate to get him through five innings."
One bright spot came in the second. Karns appeared to be in trouble when he allowed two singles to lead off the inning and then hit Ian Kinsler to load the bases. But he rebounded by getting Cameron Maybin to ground into a double play and got Miguel Cabera to ground out to end the threat.
"There wasn't really anything different I did," Karns said of getting out of the jam. "I gave up two quick singles, then I was ahead of Kinsler, and then I made a bad pitch and right there's a prime example of one of those times where I'm in my count, and I'm making a pitch that's not even challenging the hitter, it's actually getting them out of the situation. It's just stuff like that right now where I need to make my pitch."
Karns said he needs to do a better job of protecting leads, which he was unable to do Monday after Seattle's four-run second.
"I just need to get clean innings," he said. "And for some reason, that just seems to be out of my reach. I just thought I needed to do a better job of that. We're getting great run support by our offense every day."
Karns said the responsibility falls on him for not being able to take advantage of the team's powerful lineup, now that the Mariners have surrendered leads in his past three starts.
While Karns struggled, Servais said he was pleased with the way the bullpen stepped up, allowing three runs over seven innings. Joaquin Benoit in particular impressed him, as he threw scoreless eighth and ninth innings against his former team.
"It was kind of a battle of the bullpens," Servais said. "I thought our guys threw well. We just didn't get those couple big hits tonight and we left too many guys on base."
The Mariners dropped to 2-5 on their 10-game trip and 3-9 in their past 11 road games.
Kyle Beery is a reporter for MLB.com based in Detroit.