But Simmons isn't getting ahead of himself. He knows a baseball season is a long process and staying healthy and strong is the key. He missed all of 2015 and much of last season after Tommy John surgery on his right elbow derailed what had been a promising climb through the Braves' system.
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"I don't try to worry too much about performance right now," Simmons said Friday in the Mariners clubhouse at their Peoria complex. "But feeling good and being able to find my stuff and have a little command over my pitches is reassuring. I'll keep working."
Simmons adds another power arm to the Mariners' relief corps. He was being talked about as a potential closing candidate with the Braves after posting a 2.91 ERA with 23 strikeouts in 21 2/3 innings over 26 outings as a rookie in Atlanta in 2014.
But he spent the final two months of that year on the disabled list, had his elbow surgery the following season and didn't get back to the Majors until a late-season return last year when he pitched in seven games with a 1.35 ERA in 6 2/3 frames.
The 5-foot-11, 190-pounder says his arm feels stronger than ever now and his mental approach has hardened as well.
"You appreciate it more when you don't have the opportunity," he said. "I think it helped open my eyes and made me want to work smarter. Learn the ins and outs and not to overwork, but do what I need to do to stay healthy for the entire season instead of blowing it out too early or too late."
The Mariners are excited about Simmons' potential, though manager Scott Servais quietly downplayed any significance from his impressive initial throwing session Thursday.
"He looks good," Servais said. "It's an early bullpen. We don't want to put too much on it. We just want to get him comfortable here and make him feel like he's part of things and see how it plays out. … The quality of the stuff certainly looks like it's there. Get it over the strike zone, put a real hitter in there, we'll see what we've got."
Simmons finished his criminal justice degree at Southeast Missouri State during his Tommy John recovery, but his mind is fully on baseball as he looks to make his mark now with a different team in a different league.
"You could say it's a new beginning, I guess, especially since I was out of the game for a year and a half or so," he said. "Now it's going to be nice to be around a new crew and learn more and develop my game mentally and physically. It'll be nice to just finally play a full season."