O'Malley was called up from Triple-A Tacoma and will start Sunday's game in center field.
O'Malley impressed at Triple-A after a solid spring, batting .317 with a .412 OBP for Tacoma. The Mariners optioned Luis Sardinas, who has four hits in 26 at-bats and only started twice in May. O'Malley likely will be in a similar role, though if he contributes at the plate he'll get more opportunities than Sardinas.