BOSTON -- Not even motivational speeches are working for the Marlins.

Hours after owner Jeffrey Loria addressed his struggling team in a closed-door clubhouse meeting, the walls collapsed on them again at Fenway Park. They blew two separate leads before finally dropping a 6-5 decision on Thursday to cap off a series sweep for the Red Sox.

In every game of the series, the Marlins opened a first-inning lead, only to have it disintegrate into a loss. The Red Sox wiped out a 5-3 deficit with three runs in the eighth as the Marlins lost for the 13th time in their past 15 games.

“We started pretty good here,” said manager Ozzie Guillen. “But it’s not how you start. It’s how you finish. Our finish line was very narrow.”

Of all their losses in June (they are now 4-14 this month), Thursday’s might have ranked as the most bitter of all for the Marlins. Flashing their speed, they stole three bases in the first inning in grabbing a 3-0 lead. After the Red Sox tied it later, Miami went back on top 5-3 in the sixth.

But that advantage, too, failed to hold when the bullpen crumbled.

“Finally we get a lead late in the game,” Guillen said. “The bullpen has been great all year.”

It wasn’t, though, when it counted Thursday.

With the Marlins leading by two runs, Randy Choate gave up a leadoff double in the eighth to Jarrod Saltalamacchia. Edward Mujica entered and gave up a game-tying homer to Will Middlebrooks.

Ryan Kalish singled and advanced to third on a ground out. Daniel Nava drove him in with a single to make it 6-5. It was the third blown save for Mujica, who is now 0-3.

The Marlins came out of the gate running. They stole exactly as many bases in the first inning — three — as they had in all of June previously. Greg Dobbs came through with a two-out, two-run single and Omar Infante with a RBI single to make it 3-0.

But Daisuke Matsuzaka retired the next 14 batters.

Zambrano falters

Meanwhile, the Red Sox clawed back off Carlos Zambrano, who had been unable to make it out of the third inning in either of his two previous starts. He hit back-to-back batters with pitches in the fourth, both of which ended up scoring. In his five innings of work, he also walked five. One of those was the leadoff hitter in the fifth, Adrian Gonzalez, who ended up scoring as a result.

“When you hit batters and are walking people, you put yourself in a little bit of a problem,” Guillen said.

Guillen said it appears to him that Zambrano becomes too anxious when runners are aboard, which is often the case given the number of batters he has been walking.

“He gets too anxious with people on base. That’s what I see,” Guillen said. “I don’t think he’s thinking about what he wants to do. He’s just grabbing it and throwing it. We have to calm him down. We tell him to calm down. He wants to hurry and get out of the inning quick. You get out of the inning pitch by pitch. He’s rushing and trying to throw faster and harder.”

Still, the Marlins managed to get back on top.

Giancarlo Stanton launched a line-drive missile over the Green Monster to put the Marlins back out in front in the sixth, and Infante caromed a double off the tall wall to drive in another run and make it 5-3. The home run for Stanton was his 15th overall but only his second of the month.

Dismal trip

But that lead, like all the others in the series for the Marlins, failed to hold when the Red Sox mounted their comeback.

Now the Marlins return home having gone 1-5 on the trip, with their only win coming in a 15-inning marathon on Saturday in St. Petersburg. They are back to three games under .500 for the first time since May 3 when they were 11-14.

“We’ve got to step it up a notch,” Guillen said.