"I don't really know Olmos," Mariners manager Lloyd McClendon said. "I didn't see much in Spring Training. They tell me he's pitching well and throwing strikes. We need a pitcher and he's the obvious choice."
McClendon saw Olmos in action during Monday night's 4-3 loss to the Rangers, getting 1 2/3 scoreless innings from the left-hander.
Left-hander Rob Rasmussen, who was acquired from the Blue Jays in the Mark Lowe trade on July 31, was optioned to Tacoma to open a roster spot. Rasmussen pitched in all three games in Boston and threw in eight of 12 games since his acquisition, but his ERA was at 16.20 thanks in large part to giving up six runs in an 11th-inning struggle against the Rangers on Aug. 8.
"We need a [fresh] arm," McClendon said. "It was the obvious move. We really didn't have any other thing to do. He'd pitched well for us. We told him that and told him he'll be back with us at some point. I liked what I saw. He threw the ball well. He's not afraid of the competition, he competes. He did a nice job for us."
Olmos appeared in five games in relief for the Marlins in 2013. He was acquired off waivers from Miami last November, then claimed off waivers by the Rangers but returned to Seattle after Texas discovered he had an impingement in his rotator cuff.
"They sent me back here, I got healthy and now I'm happy," Olmos said before making his season debut. "I was going to be happy wherever I ended up, I was going to do my best and help the team no matter what, whether it was Texas or Seattle or whoever. And I'm glad it was Seattle."
Olmos went 1-1 with a 3.55 ERA in 20 outings -- including two starts -- with Tacoma. He was slated to start Sunday for Tacoma, but was scratched from that outing and instead flew from Oklahoma City to Arlington to join the Mariners for the first time this season.
"It feels good," Olmos said. "I believe I'm a big league pitcher. If I have confidence in myself that I'll be able to perform better. I feel like I belong."
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB, read his Mariners Musings blog, and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.