Kelley, 26, has been throwing at the team's Spring Training complex in Peoria, Ariz., in recent weeks, but has progressed to the point where he'll work out and travel with the Mariners now until he's ready for some Minor League rehab outings.
"I've been throwing successful bullpens, all fastballs, and I feel good," Kelley said after exchanging greetings with numerous teammates upon his arrival in the Safeco Field clubhouse before Thursday's game against Oakland. "I feel strong. But I'm just taking it day by day and not getting too excited."
Kelley had full Tommy John surgery when he was 18, but this time the ligament didn't completely detach and his recovery has been far quicker than normal.
He was 3-1 with a 3.96 ERA in 22 outings last season before going on the disabled list on June 25. He's appeared in 63 games over the past two seasons in Seattle.
"It definitely feels like there is a light now at the end of the tunnel, being out of Arizona, because that was just like an extension of spring without all my friends," he said. "I did what I needed to do, it was warm there, but it's definitely a good feeling being back with the team today."
As for a return when his DL stint potentially ends in 5 1/2 weeks?
"That's the plan," Kelley said. "What they do decision-wise is up to them, but based on the amount of time I have for bullpens and a rehab assignment, there's no reason right now, the way things are going, that by June 1 I wouldn't be fully game ready."
The Mariners will have to clear a spot on the 40-man roster to make room for Kelley whenever he is brought off the 60-day DL.
Third baseman Matt Mangini, who has been on the 15-day disabled list with a quadriceps injury suffered in Spring Training, was activated Thursday and optioned to Triple-A Tacoma, where he immediately was placed in the starting lineup for the Rainiers.