Workman (1-1), a second-round draft choice out of the University of Texas, collected the milestone win in his third start for the Bosox, holding the Mariners to one run on six hits over six innings.
The rookie right-hander walked one and struck out nine in the 103-pitch performance.
Pedroia's two-run blast in the second inning put Boston ahead 5-1 and his run-scoring single in the next frame handed the Red Sox a five-run advantage.
Seattle's Joe Saunders (9-10) was roughed up for six runs (five earned) on nine hits over five full frames.
Kendrys Morales went 2-for-4 with an RBI for the M's.