Armstrong (oblique) was activated from the 10-day injured list Friday.
Armstrong had been battling an oblique issue since mid-March. In a short, 14.2-inning sample last season, he recorded an excellent 1.23 ERA. The Mariners' closer job is wide open with Hunter Strickland (lat) on the 60-day injured list, though Armstrong may need a few outings to prove himself before pushing for save chances.