LONDON -- It is becoming the problem that won’t go away. And a drastic change of scenery at London Stadium didn’t fix it.

Another comfortable lead proved not to be comfortable enough for the Red Sox’s beleaguered bullpen, which had a meltdown of epic proportions in the seventh inning that led to a 12-8 defeat to the Yankees in the finale of the inaugural two-game London Series.

By losing both games here -- and giving up a total of 29 runs in the process -- the defending World Series champions trail their rivals by a whopping 11 games in the American League East. New York has taken six of the first seven head-to-head matchups this season.

• Box score

The reality of the situation was staring Red Sox manager Alex Cora in the face for two days.

“It wasn’t a good weekend on the field,” said Cora. “That’s a good offensive team, we know that. They’re a lot better than last year. The attention to detail is phenomenal. Throughout the evening, I was looking and I saw it, and right now they’re a lot better than us, so we need to get better.”

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Though Cora chose not to pinpoint one area of his team that needs to improve, it is blatantly obvious that the bullpen has become the biggest weakness.

Since June 18, the Sox have a 6.80 ERA in the ‘pen, which is among the worst marks in the Majors during that span. Prior to that date, they had a 3.97 ERA. For the season, Boston’s bullpen ERA is 4.37. That’s on pace to be among the worst ERAs a Red Sox bullpen has had in the 51 seasons they’ve played since saves became official in 1969.

“It’s tough, especially with some of our guys that were throwing the ball really good for the first 78-79 games,” said righty Marcus Walden, who started the seventh and didn’t retire any of the four batters he faced. “It’s just, I don’t think guys are pressing, they’re just missing location. There are scouting reports out. It’s not a hidden secret what we’re doing. Being able to change our approach and go back after it [is key].”

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A three-homer barrage by Xander Bogaerts, J.D. Martinez and Christian Vázquez gave the Sox a 4-0 lead in the first inning. Eduardo Rodriguez threw 115 pitches in 5 1/3 innings, but at least kept his team in the game a day after Rick Porcello recorded just one out.

Leading 4-2 after six innings, Boston relievers Walden, Matt Barnes and Josh Taylor were tagged for nine runs in the top of the seventh.

After winning the World Series last season, the Sox opted not to re-sign closer Craig Kimbrel, and instead invested their offseason spending allocation on Nathan Eovaldi and Steve Pearce, both of whom remain on the injured list. Cora was comfortable going with a closer-by-committee approach, but the plan hasn’t even come close to working of late.

Of the 34 save opportunities they’ve had this season, the Sox have converted just 17. Barnes, who was supposed to be the team’s best reliever, had a 9.69 ERA in his 15 outings in June.

Cora vowed to brainstorm for solutions between London and Toronto, where the club will resume play on Tuesday.

“It’s the nature of the 162 games and the game that we play,” said Cora. “We’ll get it right. Honestly, tomorrow is supposed to be an off-day, it’s not going to be an off-day for me. There are going to be a lot of people working on this and trying to figure out what is going on.

“Some of it is execution. Some of it is detail. It’s not a lack of paying attention to it. But people [on the other team] pay attention, too. They take advantage of situations, and I feel the last two days they did an outstanding job doing everything right. As you guys know, I’m a guy who pays attention to details and I take pride in that.

“They were better at what we do this weekend. But we’ll figure it out, trust me. We’re going to work on it. We’re going to clean it up, and hopefully when we play them again, it’s closer and we clean everything up.”

The next Red Sox-Yankees meeting is July 25, when the sides open a four-game series at Fenway Park. Between now and then, the Sox will try to get their house in order and put themselves in position for a playoff push.

“They’re playing great and they’re doing everything right. We haven’t been consistent in our game,” said Cora. “We know we can be better. We know we have a great team, but we need to stop talking about it and we need to start doing it. It’s 11 games [back] and there is no hiding. We know where we’re at. We need to finish the first part of the season playing well and then take advantage of the All-Star break, and then go out the Friday after that.”

Down 12-4, the Sox brought some excitement back to the game by scoring four runs in the bottom of the eighth. They even brought the tying run to the plate, but Rafael Devers grounded out against Zack Britton with the bases loaded to end the inning.

The damage inflicted by the bullpen was too much to overcome, even for a Boston offense that surged in the two days in London, scoring 21 runs.

“I mean, to put up the runs in general is hard to do,” said Bogaerts. “I think we put up two of the best games offensive-wise that we had this year. I mean, especially back to back. And to not win, I think that’s really rough. I think if you ask anyone, if you put up close to double-digit numbers in back-to-back games, you should probably win at least one. That wasn’t the case.”

The 108-win Red Sox of a year ago are nowhere to be found these days. There have been a couple of mini surges, but they’ve been unsustainable for a team that is just four games above .500 at 44-40.

Still, Cora says it’s not time for the Red Sox to re-evaluate their realistic goals for 2019.

“We can win the World Series,” said Cora. “We just need to play better. We need to get better in every aspect. We can talk about the bullpen or we can talk about the outfielders or we can talk about the defense or baserunning.

“We have the talent to win the World Series but we have to play better. I’ve been saying it since Day One. It better happen sooner rather than later. It’s not that we’re running out of time, but the lead [for the Yankees] is huge. It’s a huge lead, and there are other teams around us that are playing good baseball. They’re trending up, and we’re not doing that.”