The roster now stands at 28 players, with starting pitchers Hisashi Iwakuma and Taijuan Walker and reliever Stephen Pryor expected to be placed on the 15-day disabled list by Sunday's final roster deadline.
Franklin, 22, played 102 games for the Mariners last year as a rookie second baseman, but lost that job when Seattle signed Robinson Cano to a 10-year, $240 million deal.
New manager Lloyd McClendon gave the youngster every opportunity to compete at shortstop with Miller, who also was promoted at midseason a year earlier. But Miller came out hot and never slowed down. He headed into Friday's games ranked first in the Cactus League with a .439 average, .895 slugging percentage and 17 runs scored, while second to Mike Moustakas of the Royals in on-base percentage at .500.
Miller has been driving the ball all spring with 14 extra-base hits (six doubles, four triples and four home runs) in 19 games.
Franklin played well at shortstop, the position he was drafted at coming out of high school in Orlando, Fla., as a first-round pick in 2009. He hit .265 with four doubles, one home run and six RBIs in 17 games, but couldn't match Miller's production.
He'll play mostly shortstop in Triple-A Tacoma, but could also see some outfield time as well to increase his future opportunities.
"They both played extremely well, but Brad separated himself," McClendon said. "I'd be a fool if I told you he didn't. I think we all saw that. He separated himself and played extremely well. He deserves the opportunity and he's getting it. Nick didn't lose the job. It was more Brad winning it."
Though the club could make additional roster moves before the 25-man roster needs to be set on Sunday, the Mariners now appear set with their final position players with catchers Mike Zunino and John Buck, infielders Justin Smoak, Cano, Miller, Kyle Seager, Willie Bloomquist and Logan Morrison and outfielders Dustin Ackley, Abraham Almonte, Michael Saunders, Corey Hart and Stefen Romero.
The pitching also solidified with Thursday's signing of right-hander Chris Young to a one-year Major League deal, which adds a veteran at the back end of a young rotation behind ace Felix Hernandez. McClendon said Young will start Saturday's Cactus League finale and then be his fifth starter when the season opens.
Erasmo Ramirez, James Paxton and Roenis Elias will fill the other three slots and that trio has a combined 25 Major League starts between them, with Elias making the jump from Double-A ball and Paxton having pitched just four games for the Mariners last September.
Elias, a 25-year-old Cuban defector who earned a job by going 3-0 with a 2.04 ERA in five Cactus League games, was thrilled to get his first Major League opportunity.
"I didn't understand everything he said because most of it was in Spanish, but I think in the end he tried to kiss me," McClendon said. "I figured he was happy at that point.
"Getting here was a major accomplishment," McClendon said. "When we talk about the lights coming on, I don't think there's anything that's going to faze this young man. He came off a boat, where he was fighting for his life to get here. I think he'll be just fine. I think he's got a bright future ahead of him."
All-Star right-hander Iwakuma and top prospect Walker are recovering from injuries and could be back sometime in late April, but for now the youngsters will get their chance to shine along with Young, who hasn't pitched in the Majors since 2012 due to shoulder problems.
The bullpen is set now as well with closer Fernando Rodney and fellow right-handers Danny Farquhar, Yoervis Medina, Hector Noesi, and Tom Wilhelmsen, along with left-handers Joe Beimel and Charlie Furbush.
McClendon said Beimel brings a veteran presence, while Noesi earned the long reliever position with a strong spring as he posted a 2.77 ERA in six outings. Noesi is out of Minor League options and would have been exposed to waivers if he'd been sent down.
"He threw the ball extremely well," McClendon said. "I don't think anybody will argue that fact. I thought he made drastic improvements over last year. The staff was very impressed and he deserved that opportunity. The young kids, Leone and Smith were sent out. They threw well. They're young, they need a little more seasoning, but I think they'll be knocking on the door very soon. They're very impressive."
Leone, packing his bags to head to the Minor League clubhouse, said he understood the process.
"It was a move that had to be made and I completely understand," said the hard-throwing 22-year-old. "I'll work my butt off down there and try and get back up here, that's all. I did everything I could. That's the biggest thing. I just came in trying to throw and prove to myself and everybody else that I belong here. So it's not at this time, but hopefully it'll be sooner rather than later."
Beimel and Elias were non-roster invitees who had to be added to the 40-man roster, so outfielder Xavier Avery and shortstop Carlos Triunfel were designated for assignment to clear spots.