The division champion Athletics handed Seattle its 90th loss of the campaign, the fourth time in six seasons the Mariners have suffered hat many setbacks.
Moss hit a three-run blast in the first inning and, after Seattle crept within a run in the sixth, Norris hit a two-run shot during a three-run seventh. Norris also had an RBI double in the eighth.
Bartolo Colon (18-6), making his final start before the postseason, allowed two runs on three hits with eight strikeouts in six innings. Only Detroit's Max Scherzer, with 21, will finish with more wins in the American League than Colon.
Felix Hernandez (12-10) wound up with the loss, giving up three runs on five hits in six innings.