GM Jerry Dipoto says organization’s top minor-league starter the last two seasons is better suited to be a reliever in the majors than a starter and began that process with an eighth-inning appearance for Class AA Jackson.

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To the people in attendance at Regions Field in Birmingham, it might not have seemed like a big deal when Edwin Diaz entered the game for the Class AA Jackson Generals to pitch the eighth inning.

But for the Seattle Mariners, it represented a major shift in the future of one of their top pitching prospects. Diaz, the organization’s minor-league starting pitcher of the year for the last two seasons, began the process of being converted to reliever with that one-inning appearance.

General manager Jerry Dipoto confirmed the change late Tuesday night and discussed it with the media before Wednesday’s game.

“The guy has a chance to be a pretty good reliever,” Dipoto said. “Edwin has plus fastball velocity, plus fastball life and what at times is a plus breaking ball. The changeup has never really been easy for him. It’s not the most conventional arm action and delivery you will ever see. So the likelihood of him picking up that third pitch was maybe a little bit more remote.”

Diaz, 22, was a third-round selection in the 2012 draft out of the Caguas Military Academy in Puerto Rico. This season he was 2-3 with a 3.10 ERA in five starts with the Generals. But the lack of a third pitch and questions about his durability because of size — 6-3, 170 pounds — were reasons for the change.

“We felt like as a starter he’s mostly 90-94 mph with a good slider,” Dipoto said. “What happens when we dump him into a bullpen? Do we have a chance to get that back-end dynamic arm? And does that supersede the ceiling that he would have as a starter? As nice as his progression has been as a starter, we felt like his ceiling was probably more back of the (starting) rotation because of the third pitch and the general wonder about how he could handle the innings because it’s not the largest frame among the pitchers in our system. But as a reliever, if he can acclimate himself to the bounce back and show the resiliency to be a bullpen guy, does the stuff tick up?”

It did in his first outing of a two-week schedule of appearances to get him used to the role.

“He was up to 98 mph and sitting on 96 mph and looked every bit of what we hoped it would look like,” Dipoto said. “Now we have to see if it looks like that in outing No. 2.”

This isn’t the first analysis of Diaz profiling as a reliever. Multiple scouts from opposing organizations have had similar projections.

“We don’t take any evaluation lightly,” Dipoto said. “And coming in, the general evaluation with Edwin Diaz is that it was very likely more to a major-league reliever than a major-league starter. We didn’t want to jump to any conclusions. We watched him through spring training. There’s a reason we didn’t bring him to major-league camp. It was so we could cultivate him slowly and make a determination of what his role was going to be.”

Why not let Diaz start until needed as a reliever?

“Having done that job and having been developed as a starter through Double A, if you are going to be a major-league reliever with what’s required of major-league relievers, you have to be acclimated to that role before you are just thrown into it,” Dipoto said. “You can’t take a guy from your starting rotation, who has accrued 130 to 140 innings and just dump him into the bullpen and think you are going to pitch him three times a week in leverage situations. It doesn’t work that way. We are taking this step.”

Note

Joaquin Benoit and Charlie Furbush both threw bullpen sessions before the game. Dipoto sat and watched them carefully.

“They looked great, both of them,” Dipoto said. “Furbush was extremely aggressive through the ball. That was the best we’ve seen Joaquin Benoit since he signed with the club. The ball was really carrying out of his hand. As I wanted to believe when I went out there, he’s very close to being back — hopefully by the time we start this next road trip.”

If the two relievers feel well after the bullpen sessions, they will face live hitters. Benoit will throw a simulated game on Saturday at Safeco Field. Furbush will throw live batting practice at Cheney Stadium in Tacoma sometime this weekend. If that goes well, Furbush will go to Peoria to start an innings progression similar to spring training.

“There was a lot of enthusiasm after their last sessions, so that’s why I made the trek out there (to the bullpen) to see for myself,” Dipoto said.