Karns, the Mariners' fifth starter who will make his first start Saturday against the A's at Safeco Field, held the Rockies to three hits and three runs in six innings and finished the spring with a 5.42 ERA.
"It was definitely nice to get my work in my last start and feel good about where I'm at," said Karns. "I was trying to do too much at the beginning [of spring], but I've kind of found my rhythm and am settling into my own right now."
"Karns was really sharp. It was a nice way to wrap it up down here," said Mariners manager Scott Servais, whose club finished spring with a 16-14-3 record.
"We played a lot of games. We made it through. I think we're in a pretty good spot. Everybody is healthy, we got most of the bullpen guys an inning today, so we're ready to roll."
Rockies starter Jordan Lyles, announced earlier Saturday as the starter for Friday's home opener against the Padres, gave up one run in three innings of fleeting command. Lyles threw strikes on 15 of his 30 pitches. He escaped the first inning by working Robinson Cano into a double-play grounder, but paid for walking Kyle Seager with two out in the third when Cano doubled. Cano finished spring with a .368 batting average. Lyles finished spring with a 7.11 ERA.
"I didn't give up as many runs," Lyles said. "I walked three people, which is not ideal. Going into the season healthy, that's exciting. I'm just looking for a healthy season."
Rockies third baseman Nolan Arenado went 1-for-2 to end Cactus League play with a .542 batting average.
Up next for Mariners: Felix Hernandez takes the hill for his team-record ninth Opening Day start on Monday when Seattle faces off against Rangers left-hander Cole Hamels in a 1:05 p.m. PT game at Globe Life Park in Arlington. Hernandez is 6-0 with a 1.49 ERA in eight Opening Day starts and he was 5-0, 1.83 last year against Texas. The game will be televised on MLB.TV.
Up next for Rockies: Lefty Jorge De La Rosa, the club's all-time leader in wins and strikeouts, will open the regular season against the D-backs and their free-agent coup, righty Zack Greinke, on Monday at 7:40 p.m. MT. The game will be televised on MLB.TV.
Thomas Harding is a reporter for MLB.com. Follow him on Twitter @harding_at_mlb, listen to podcasts and like his Facebook page. This story was not subject to the approval of Major League Baseball or its clubs.