Montgomery, who finished 4-6 with a 4.60 ERA in 16 starts for the Mariners last season, has not allowed a hit in three innings in his first two relief appearances, including a perfect ninth inning Saturday night in a 6-1 loss to Oakland.
"Mike's been off to a really good start," said Mariners first-year manager Scott Servais. "I'm really excited. Obviously, it's a transition for him. Sitting down with him in Spring Training and seeing it kind of evolve there, confidence starting to come. He could certainly work into a key role in our bullpen. Being left-handed and the stuff he's got, it's really advantageous for us to get to the point where we can use him regularly."
In the Minors, Montgomery started 161 of his 166 appearances, with three of the relief outings coming in his first season in 2008 in the rookie league. His two complete games last season matched his entire Minor League total.
Montgomery, a first-round Draft pick by Kansas City in 2008, started fast last season after being called up in early June, but faltered and was sent to Triple-A Tacoma at the end of August.
With Montgomery out of Minor League options, the Mariners moved him to the bullpen rather than risk a waiver claim.
"For where we're at and how our team's put together, we've got other guys we like starting ahead of Mike," Servais said. "It doesn't mean he can never be a starter again. But right now at this point in his career, I think Mike wants to stay in the big leagues. Where he's at in his career, I think he's willing to do whatever he can to stay in the big leagues and help us win ballgames. And, the way we're built, that's out of the bullpen."
Montgomery said the switch has been both a physical and mental change.
"Physically, it's definitely a difference," said Montgomery, who has struck out five and walked one in three innings of relief. "I haven't had to go back-to-back in the season yet. In talking with a lot of these other relievers, they say it can be physically taxing. If you get up and warm up and don't go in the game, those still add up. That's going to be a challenge I'm definitely going to have to face."
In game situations, Montgomery said he still is trying to determine the approach that best works for him.
"When you're starting, you have the four days of preparation and you know who you're going to face," he said. "But, in the bullpen, you might pitch or you might not. You don't know, so you don't really get to think about it. So, for me, it's been a pretty easy transition in that sense. If the phone rings and they call for me, I get ready and go.
"When you get out there, it's just trusting that your stuff's going to be there when you get in the game," Montgomery said. "That's what everyone in the bullpen said. Don't spend the extra five or 10 minutes. Just trust that when you go out there, it's going to be there ... you don't need to overdo it in the bullpen."