BOSTON — With the Boston bullpen struggling to put opponents away, the playoffs hopes of the Red Sox are slowly diminishing. The Red Sox lost another game in the AL Wild Card standings on Monday night after the bullpen couldn’t close the door on the Houston Astros. 

The Red Sox let a 4-3 lead slip away in the bottom of the eighth inning in Houston when Lucas Sims gave up the game-tying run on an RBI single off the bat of Mauricio Dubon. Sims surrendered two hits and issued two walks in his inning of work, and was tagged with his second blown save over nine appearances since arriving in Boston at the trade deadline. The righty owns a 6.23 ERA and 1.50 WHIP over 8.2 innings for the Red Sox.

The Boston bats went quietly in the top of the ninth, when Alex Cora turned to closer Kenley Jansen for the bottom of the inning. He made quick work of Yordan Alvarez, whom he fanned on three straight pitches, but Yainer Diaz returned the favor when he took the first pitch he saw from Jansen and launched it 400 feet to left-center for a walk-off homer. 

It was the first hit surrendered by Jansen since July 27.

The Boston bullpen has now allowed 89 runs since the All-Star break, which is by far the most in all of baseball. Even the lowly White Sox haven’t been as woeful, allowing 71 runs over that span. Boston relievers have surrendered 26 homers and been charged with a dozen blown saves — to just four saves — while touting a 6.93 ERA over that stretch. They lead the Majors in all three of those statistics.

The unofficial second half started with the Sox getting swept by the Dodgers, losing two games in which they held leads in the eighth inning. Last week against the Rangers at Fenway, the Red Sox lost a game they led by three runs with Texas down to its final out.

Sims isn’t the only one of Craig Breslow’s deadline acquisitions to falter out of the Boston pen. Luis Garcia has been even more dreadful, touting a 14.09 ERA over his 7.2 innings. He has allowed at least one run in six of his seven appearances with Boston.

The bullpen’s demise is an unfortunate development for the Red Sox, with the team’s starting rotation finally turning things around as of late. But the team’s relievers were overworked when the starters struggled during June and July, and now the team if feeling the effect of that bullpen burnout.

With the bullpen coughing up late leads, Boston’s playoff hopes are now on life support. The Red Sox held a two-game lead over the Royals for the final AL Wild Card spot ahead of the break. But with Monday’s defeat and a Royals win, Boston now trails Kansas City/Minnesota by 4.5 games with 38 remaining in the regular season. The Royals have now won five straight, and are tied with Twins for the second Wild Card slot.

“I look at the standings, the scoreboard all the time,” Cora said Monday night. “I know Kansas City won. I watch. I’m a baseball fan, and I know where we’re at. But I’m confident in where we are, pitching-wise. If we continue to do that, we’ll be OK. Our starters are throwing extremely well.”

The starters are throwing well, but the bullpen is squandering Boston’s impressive starts. Tanner Houck returned to form Monday night and held the Astros to two runs over six innings, but it was wasted by the eighth inning. The Red Sox have now lost six straight Houck games, which is not a recipe for making the postseason.

Some bullpen reinforcements could be on the way, with Justin Slaten and Liam Hendriks potentially joining the fray in the coming weeks. But there is no guarantee they’ll be effective, and by the time they potentially enter the mix, it may be too late for the Red Sox and their postseason hopes.

The Red Sox have two more against the Astros — who have won the last four against Boston — before returning home for three against the Arizona Diamondbacks, who are 20-8 since the break. At least there is a lighter stretch of the schedule on the horizon, with series against the Blue Jays, Tigers, and White Sox to end August and start September.

But the Red Sox have no margin for error right now, and cannot afford to just stay afloat over the next five games. With the bullpen scuffling, Boston’s postseason dreams could be dashed before that easier stretch even arrives.