Wednesday's transaction will allow the 26-year-old Blash to remain in the Padres' system in the Minors. He has been assigned to Triple-A El Paso.
"I think we saw what he could do last year when he got everyday at-bats at Triple-A, and that's why we picked him up in the Rule 5," said Padres manager Andy Green. "We're thrilled we were able to work out a trade."
Between Double-A and Triple-A in the Mariners system last season, Blash batted .271/.370/.576 with 32 homers. That power was also on display during Spring Training, when four of his 10 hits were home runs. But with limited playing time, Blash never found a rhythm at the big league level.
Green spoke to the importance of getting Blash everyday reps, and he noted that Blash could potentially serve as a callup later in the season.
"It was a tough hand to be dealt for a guy like him, coming off the bench," Green said. "As big as he is, long-limbed guys have a hard time getting timing down, especially when they haven't had success at the Major League level before. Those were tough at-bats for him, and nobody really wanted to judge him strictly on those."
AJ Cassavell covers the Padres for MLB.com. Follow him on Twitter @ajcassavell. This story was not subject to the approval of Major League Baseball or its clubs.