Reddick's 10th-inning, game-winning single against the New York Yankees last Sunday gave the Red Sox the lead in the AL East ahead of their rivals, and his homer on Friday extended the lead to two games. The Yankees lost to Tampa Bay earlier Friday night.
Reddick's sixth homer was the cap to a three-homer night by the Red Sox off Seattle starter Blake Beavan (3-3). David Ortiz and Jed Lowrie also homered for Boston.
Seattle knocked around Boston starter John Lackey for 10 hits, but Lackey (11-8) still managed to pick up his seventh straight victory.
Ortiz added an RBI single in the seventh that finally knocked out Beavan and concluded the worst start of his young career. Beavan was tagged for six runs and 11 hits, snapping a string of six straight starts going at least six innings and giving up three earned runs or less. He struck out one and walked one but allowed a trio of costly homers.
None was more damaging than Reddick's shot in the sixth. Beavan was ahead in the count 1-2 when he tried to sneak a fastball past Reddick down and in. Reddick quickly dropped the bat head and rattled the patrons eating dinner in the right field cafe.
Mike Aviles also had a sacrifice fly as the Red Sox won for the fifth time in six games.
Boston needed all the offense because Lackey again wasn't sharp. For the third time in his last six starts, Lackey allowed double figures in hits and he was done after giving up a leadoff single to Mariners rookie Dustin Ackley leading off the seventh inning.
Mike Carp followed with a single off reliever Franklin Morales, but Morales later got Adam Kennedy looking and Daniel Bard struck out Miguel Olivo to end the threat.
Bard got through the eighth before Jonathan Papelbon worked the ninth for his 27th save in 28 chances.
Lackey's been helped during his win streak by getting plenty of run support. His seven straight wins span eight starts and in those outings, the Red Sox have averaged six runs while Lackey is in the game.
Seattle loaded the bases in each of the first two innings thanks to six hits off Lackey. They managed only three runs as Lackey wiggled out of both jams without letting the game turn into a blowout early. Carp had a two-run single in the first, extending his hitting streak to 12 games, and Ackley had an RBI single in the second.
Carp also had a two-out RBI double in the fourth inning.
By the fifth, Lackey was setting down the Mariners in order for the first time and giving the Red Sox offense a chance to rally.
Seattle lost first baseman Justin Smoak in the second inning after he fractured his nose when Jarrod Saltalamacchia's grounder bounced up and hit him in the face.
Smoak was down on the dirt for a couple of minutes and was bleeding after Saltalamacchia's one-hop shot appeared to hit off the bill of his hat and catch the bridge of his nose. Saltalamacchia ran to first with his hands on his head after seeing Smoak fall to the ground.
Smoak later underwent a CT scan at a local hospital. He had returned to the lineup Friday after missing five games with a sore left thumb.
Boston was also without third baseman Kevin Youkilis and shortstop Marco Scutaro. Both were in the original lineup only to be scratched later with stiff backs.
Notes
Sgt. 1st Class Leroy Petry, who was recently awarded the Medal of Honor by President Barack Obama, was honored before the game by the Mariners. His son Austin threw out the first pitch. … Injured Boston OF J.D. Drew (shoulder) hit during batting practice Friday and is scheduled to do it again Saturday. … Boston RHP Josh Beckett starts on Saturday in his fourth attempt at getting win No. 10 this season. Beckett beat Seattle 3-1 on July 23 for his ninth win. … Seattle RHP Felix Hernandez has given up eight earned runs in 13 1-3 innings pitched this season against the Red Sox.