SCOTTSDALE, Ariz. -- A year ago, he was converting from starter to reliever, a guy with a power arm and two-pitch potential who the Mariners saw as a possible bullpen boost in the future. But first, he had to prove himself at Double-A before making the jump to the big leagues.
Edwin Diaz? Yeah, the Mariners' closer fits that description. But so does Dan Altavilla, another key component in this year's Seattle bullpen.
Altavilla, a powerfully-built 24-year-old, hasn't gotten the same attention as Diaz, whose electric stuff elevated him to the closing role in the final months of 2016, as well as on the international stage when he pitched for Puerto Rico in the World Baseball Classic.
But Altavilla, the Mariners' No. 9 prospect per MLBPipeline.com, could play a significant role for Seattle this season as well. Though he's pitched only 12 1/3 innings in the Majors after a late-season call-up last year, the 5-foot-11, 200-pounder has thrown as well as anybody in camp this spring, posting a 2.70 ERA with 11 strikeouts and two walks in 10 innings.
"Altavilla has really taken a step forward," manager Scott Servais said. "I hope Danny works his way more toward the back of the game than the beginning. I think he's got that kind of upside."

The Pennsylvania native was plenty impressive last year as well, allowing just one run, with 10 strikeouts and one walk, in his 12 1/3 innings over 15 appearances. He was added to the big league team on Aug. 27.
With his limited experience, Altavilla still carries rookie status. Along with right fielder Mitch Haniger, Altavilla is a rookie who could play a significant role on a largely veteran team.
Altavilla took nothing for granted this spring, expressing relief after hearing he had made the final 25-man squad on Friday.
"It's hard not to think about it," Altavilla said of the roster battle. "But when it comes down to it, you've got to perform and you've got to show up to pitch. Everyone knows there's competition in the clubhouse. But you can't really think about it, or it gets in your head. We just like to come in here and have fun and get to know each other."
Now, Altavilla will be one of the eight relievers opening the season at Minute Maid Park on Monday against the Astros.
"I'm pumped to start the season off in Houston with the big league team," Altavilla said. "I'm just going to take last year and run with it, pick up where I left off here. Just keep throwing strikes and getting guys out."

If Altavilla keeps doing that, don't be surprised to see the youngster emerge soon as an eighth-inning set-up option before Diaz. As Servais said, Altavilla has that type of potential.
But it's also important to remember the former Mercyhurst College starter is still getting acclimated. Monday will be Altavilla's first time experiencing Opening Day with a big league team. And he'll soak that in like everything else he's absorbed in the past year.
"Just seeing it on TV is unbelievable," Altavilla said of Opening Day. "So being able to live in that moment is going to be something special and something I won't ever forget."