Jacoby Ellsbury and Dustin Pedroia homered in the second, giving Workman a cushy 5-1 lead that the young right-hander never squandered in just his third start in the big leagues. He allowed six hits, three of them in the sixth when Seattle loaded the bases with one out before Workman (1-1) ended the threat with back-to-back strikeouts.
Joe Saunders (9-10) allowed six runs over five innings for Seattle, including two in the first as the Mariners set themselves back with an error and a passed ball.
Pedroia drove in three runs, Shane Victorino had three hits and scored three runs, and Jarrod Saltalamacchia added a two-run homer in the eighth for Boston, which left just three runners on base.
The Red Sox led 2-1 after the first, before breaking broke it open with three more runs. Ellsbury hit a one-out homer into the Mariners' bullpen, which appeared to be in for a busy night.
It was Boston's fifth hit off Saunders, who was lucky Ellsbury's fifth homer of the season was a solo shot. Jose Iglesias led off the inning with a single, but tried to stretch it into a double and got caught in a long rundown.
Victorino followed with a single, then Pedroia hit one out to left for a 5-1 lead.
Saunders allowed one more run in the fourth when Victorino doubled and scored on a single by Pedroia.
Seattle took a 1-0 lead in the first when Nick Franklin doubled with one out and scored on a single by Kendrys Morales.
The Mariners loaded the bases with one out in the sixth on consecutive singles by Kyle Seager, Morales and Raul Ibanez. Workman struck out Michael Morse for the second out, then got Justin Smoak swinging on his 103rd pitch of the night to end the threat.
Workman's previous high for strikeouts was five against Oakland in his first career start on July 14, when he left with the score tied at 2 in the seventh and didn't figure in the decision.
His only other start was last Monday against Tampa Bay, when he allowed two runs in six innings but got absolutely no offensive support in the 3-0 victory for the Rays.
Notes: The Red Sox held a pregame ceremony honoring former manager Joe Morgan, who threw out the ceremonial first pitch. The Red Sox won their first 12 games after Morgan took over midway through the 1988 season and went on to win the American League East during the era dubbed "Morgan Magic" in Boston. ... The three-game series continues Wednesday with Seattle ace Felix Hernandez (11-4) facing Boston RHP John Lackey (7-8). ... Manager John Farrell said before the game that Boston hoped to have RHP Clay Buchholz (right shoulder) back in the rotation, but could not say how soon. "That would be as good of an addition as we can make at any deadline," Farrell said. ... Saunders opened July with four straight wins and ended the month on a two-game losing streak. ... Iglesias was applauded after his baserunning blunder in the second. He avoided the tag at second with a slide beyond the bag, then went back and forth until Seattle eventually got him on a 7-4.