The Mariners optioned Nittoli to Triple-A Tacoma on Thursday.
The 30-year-old Nittoli's first stint in the big leagues lasted just under a week after he was brought up from Tacoma last Friday. He made his MLB debut Wednesday against the Rockies, giving up two runs over one inning. Seattle will call up Keynan Middleton from Triple-A to replace Nittoli in the bullpen and on the 26-man active roster.