Once again, poor pitching lead to the Marlins' 13th loss in their past 15 games as the bullpen surrendered three runs in the eighth. Edward Mujica served up a game-tying two-run homer to Will Middlebrooks and Daniel Nava put the Sox ahead with an RBI single.
Middlebrooks jumped on a 2-2 fastball and sent it to dead center for his eighth homer.
"I was thinking, 'Don't get out.' I knew it was his go-to pitch, so I was trying to see it early and get a good piece of it," said the rookie, who went 3-for-4 with four RBIs.
Miami president and CEO Jeffrey Loria met with the club before batting practice on Thursday, holding a closed-door meeting for roughly 15 minutes. Nonetheless, the team fell to 4-14 in June.
The Marlins scored five runs for the third time in as many nights, including a three-run first inning, but again it wasn't enough.
"We've just got to play relaxed," said outfielder Giancarlo Stanton. "Today we jumped up with those three runs and still kind of felt a little shaky. It wasn't like, 'Hey we got this.' The result ended that way. I'm not worried about losing this many games or playing this bad."
Stanton broke out of a 1-for-20 slump with a go-ahead home run in the sixth inning. Stanton crushed a 1-2 offering from Red Sox starter Daisuke Matsuzaka over the Green Monster for his 15th homer of the year and his first since June 7 vs. the Braves.
But the lead did not last long. Still, the Marlins thought they could avoid a sweep after Stanton's blast that made it 4-3.
"Yeah, because I believe in my bullpen," Guillen said. "We had the matchup we wanted, but they beat our matchups."
Carlos Zambrano had a chance to win his first game in three starts, but that went out the window in the eighth. The right-hander allowed three runs on five hits in five innings. He walked four, hit two batters and struck out three.
The Marlins scored in the first inning for the third time in the series. Greg Dobbs lined a two-run single to right, and Omar Infante followed with an RBI single to give Miami a 3-0 lead.
From there, Zambrano did what Mark Buehrle and Ricky Nolasco couldn't and preserved the lead for nearly five innings. But the same didn't hold true for the bullpen.
The Red Sox scored two in the fourth after Zambrano plunked the first two batters he faced, Cody Ross and Jarrod Saltalamacchia. Zambrano's second pitch to Ross appeared to hit his bat, but home-plate umpire Mike Dimuro awarded the former Marlins outfielder first base.
"He acted like it hit him and the umpire made the decision and there's nothing I can do about it," Zambrano said. "He's a good actor."
Middlebrooks made Zambrano pay with an RBI single and Mike Aviles added a sac fly.
Boston tied the game at 3 with another RBI single from Middlebrooks in the fifth.
Guillen said Wednesday that he wanted his team to make Matsuzaka cry on the mound in his third start since recovering from Tommy John surgery. Miami didn't quite accomplish that, but the club made the right-hander labor through a 33-pitch first inning.
After Miami scored its third run, Matsuzaka retired the next 14 batters he faced until Stanton took him deep.
"He was a little shaky in the first inning and besides that he did a great job," said Stanton, who went 2-for-3 and scored two runs. "He was working in and out and using all of his pitches and had our timing a little off."
Matsuzaka was removed in favor of Andrew Miller following Stanton's blast. Dice-K allowed four runs on four hits in 5 1/3 innings, striking out four against one walk.
The Marlins tacked on another run in the sixth on an RBI double from Infante that made it 5-3. Miami held a lead in all three games of the series but it couldn't hold off Boston.
"We start pretty good here," Guillen said. "It's not about how you start, it's about how you finish. Our finish line was very narrow."
At 33-36, Miami is three games under .500 for the first time since May 3, when the club was 11-14.
"We have to come back with a winning attitude," Guillen said. "I expect my team to fight. I will make them fight."