Daniel Nava's RBI single capped off a six-run ninth inning for the Red Sox, who rallied past the Seattle Mariners, 8-7, to complete a three-game sweep.
Boston, which was coming off a 5-4 win in 15 innings on Wednesday, has now won in walk-off fashion a major league-best 11 times this season.
Holding what seemed to be a comfortable 7-2 lead, Seattle sent Tom Wilhelmsen to the mound to start the ninth. Nava led off with a walk, moved to second on Ryan Lavarnway's single and scored on Brock Holt's double to left. Jacoby Ellsbury followed with a walk to load the bases.
Oliver Perez (2-3) was called in from the bullpen, but his luck was the same. Shane Victorino hit a two-run single to right-center field and Dustin Pedroia added an RBI single to left, cutting the gap to 7-6. The first out of the frame finally came when David Ortiz struck out swinging.
Yoervis Medina was then called upon to try and save Seattle. Jonny Gomes had other plans with an RBI single to center. Medina threw four straight balls to Stephen Drew to fill the bags. Nava came up to the plate for the second time in the inning and delivered with the game-wining hit to deep center field.
"Guys care about each other, guys want to win," Pedroia said. "We're going to fight until the end. We understand in the big leagues it's tough, but we're going to give everybody everything we got."
Victorino hit a solo homer in the eighth for the Red Sox, who have won six straight against the Mariners.
Steven Wright (2-0), who was recalled from Triple-A Pawtucket prior to the game, gave up two hits over three scoreless innings of relief to pick up the win. Boston starter Ryan Dempster had a rough outing, giving up seven runs on nine hits while walking five over six innings.
Henry Blanco hit a grand slam for Seattle, which has lost five of six. Kendrys Morales went 4-for-5 with an RBI and a run scored and Justin Smoak and Kyle Seager each knocked in a run.
Felix Hernandez got the start for the Mariners and allowed one run on six hits while striking out eight over seven frames.
"Well played ball game by us up until that last inning," Mariners acting manager Robby Thompson said. "Great job by Felix again...unfortunately in the ninth inning we didn't get the three outs that we needed."
Seattle jumped out to a 1-0 lead in the first inning. Brad Miller tripled to right and raced home on Seager's bunt single. The visitors went on to load the bases later in the frame, before Endy Chavez grounded out.
The Mariners tacked on another run in the third. Seager led off with a walk, moved to second on Morales' base hit and scored on Smoak's single to right.
The Red Sox got one run back in the bottom half. Ellsbury doubled to left- center field, moved to third when Victorino flied out and scored when Ortiz flied out to left. Pedroia, who walked, was thrown out at second on the play for a double play.
Seattle appeared to pull away with a five-run fifth. Seager led off with a triple to right and raced home on Morales' single to right. Smoak doubled and Dustin Ackley walked to load the bases with two outs. Blanco then cleared the Green Monster to make it a 7-1 contest.
Victorino's homer in the eighth set the stage for another walk-off victory. The Red Sox have two straight walk-off wins for the first time since August 2-3, 2011.
The Red Sox have 11 walk-off wins in a season for the first time since 1978. Their franchise record is 13 in 1940 ... Boston added pitcher Jake Peavy to the active roster and optioned pitchers Brandon Workman and Jose De La Torre to Pawtucket ... The Red Sox (66-44) are a season-high 22 games over .500 ... This was Boston's ninth straight win over the Mariners at Fenway Park, extending a club-record home winning streak against Seattle ... It was Seattle's second straight loss in walk-off fashion, and eighth overall this season ... Blanco's grand slam was the third of his career.
08/02 02:14:31 ET