Dustin Pedroia and Jarrod Saltalamacchia each hit a two-run homer, while Brandon Workman won his first major-league game, as Boston dismantled Seattle, 8-2, in the opener of a three-game series from Fenway Park.
Pedroia ended up with two hits and three RBI and Shane Victorino finished with three hits and scored three times for the Red Sox, who have won three of their last four.
Boston remained a half-game behind Tampa Bay in the AL East, as the Rays opened up their series against Arizona with a win.
Workman (1-1) scattered six hits and one run over six effective innings, fanning a career-best nine batters with one walk.
"Hopefully tonight is the first of many wins in his career," said Boston manager John Farrell about Workman. "As we've seen in the three starts he's made, once he gets through the first three innings he starts to get a good rhythm going."
Following the game Boston acquired right-handed pitcher Jake Peavy in a three- team deal with the Chicago White Sox and Detroit Tigers.
The Red Sox received the former Cy Young Award winner and sent minor league pitchers J.B. Wendelken and Francelis Montas and infielder Cleuluis Rondon to the White Sox.
Boston also received right-handed pitcher Brayan Villarreal and outfielder Avisail Garcia from the Tigers for shortstop Jose Iglesias. The Red Sox then sent Garcia to the White Sox.
Kendrys Morales hit an RBI single and Henry Blanco an RBI double for the Mariners, who began a six-game road trip with their fourth loss in six outings.
Joe Saunders (9-10) was battered for nine hits and six runs -- five earned -- over his six-inning start.
"It didn't look like he had his best stuff out there," said Seattle acting manager Robby Thompson about Saunders. "He just wasn't getting the ball down in the zone and getting some of those calls."
Jacoby Ellsbury's one-out homer into the right-field bullpen made it 3-1 for Boston in the home second. Victorino then singled and when Pedroia cleared the Green Monster with two down, the hosts led by four.
In the fourth, Victorino doubled with two down and scored on a Pedroia single, but the inning concluded when Pedroia took a wide turn at first and was thrown out trying to scramble back.
Workman escaped a jam in the sixth, fanning both Michael Morse and Justin Smoak swinging with the bases loaded. Kyle Seager, Morales and Raul Ibanez all singled with one down to load the bases, but the 24-year-old right-hander stayed cool and exited with no further damage.
Mike Napoli's one-out single in the eighth was followed by a two-run blast from Saltalamacchia for an 8-1 game.
Pedro Beato was dented in the ninth as Blanco plated Smoak with a two-out double to get the M's within six, but that was all the visitors had left in the tank.
A Morales two-out single scored Nick Franklin to put the Mariners on the board in the first, but the Sox responded with two in the home half as Victorino scored on a passed ball and a David Ortiz single plated Pedroia.
Workman's previous high was five strikeouts, in a July 14 no-decision at Oakland ... The Red Sox have won four of the five meetings this season with Seattle ... Prior to the contest, the Mariners activated Morse from the 15-day disabled list and designated outfielder Jason Bay for assignment.