It was the Mariners' fifth straight win.
Boston lost for the fourth time in five games after winning eight of nine.
Seattle's Milton Bradley had an RBI double before being ejected a few minutes later and the Mariners' bullpen pitched the final 3 1/3 innings. Seattle's pen has held opponents scoreless for the last 13 1/3 innings.
The Red Sox went hitless the final five innings — two against the bullpen — in Friday's 5-4 loss.
Fister (2-3) allowed five hits, walked five and fanned four.
Aaron Laffey pitched 2 1/3 of one-hit relief and Brandon League got the final three outs for his seventh save in seven attempts.
Bradley's double gave the Mariners a 1-0 lead in the second, halting a 15 1/3 inning scoreless stretch by John Lackey (2-3). Ichiro Suzuki walked and Chone Figgins singled before Bradley doubled just inside the left field foul line.
Bradley, standing at second following his double, was ejected by second base umpire Gerry Davis after Miguel Olivo was out on a close grounder at first. Manager Eric Wedge had just gone back to the dugout after arguing the play with Tim Tichenor, but was not tossed.
Jack Wilson's sacrifice fly made it 2-0 in the sixth.
Lackey gave up two runs, seven hits, walked four and struck out three in six innings.
Fister escaped a bases loaded jam in the first and stranded Jacoby Ellsbury at second after his leadoff double in the third.
But his biggest escape act came with the help of the Red Sox when he loaded the bases with no outs in the fifth.
Jarrod Satalamacchia led off with a double before Ellsbury and Dustin Pedroia walked. Adrian Gonzalez then lined into a double play, with Ellsbury getting caught diving back to second and Kevin Youkilis fouled out. The Red Sox had first and third with two outs in the sixth before Laffey got the final out.
In the first, Boston loaded the bases with one out before David Ortiz struck out swinging and J.D. Drew flied out.
Notes:
Seattle's Justin Smoak went 0-for-4, snapping his 11-game hitting streak. … Boston veteran knuckleballer Tim Wakefield will start Sunday against Felix Hernandez. The original scheduled starter, Clay Buchholz, was pushed back a day after he left the park Friday when he wasn't feeling well. … The Mariners close a six-game road trip Sunday and have Monday off before opening a three-game series against Texas. … Fister allowed just one run and four hits over six innings in his previous start Sunday against Oakland. … Lackey has given up just three earned runs in 20 innings over three starts after giving up 15 runs total in his initial two of the season.