Seattle’s bullpen is, indeed, human.

The typically sturdy relief corps blew a late lead in the Mariners’ 7-5 loss to the Astros on Wednesday at Minute Maid Park, allowing four runs in the bottom of the eighth and wasting Justin Dunn’s solid outing.

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“That one stings a little bit tonight,” manager Scott Servais said.

Seattle entered the eighth inning with a two-run lead, having played a fairly well-rounded game. Rafael Montero, who hadn’t pitched in nearly a week, was assigned the frame, tasked with serving as a bridge to the ninth.

Montero started his night well enough, managing to neutralize some heavy hitters. The right-hander got Michael Brantley to ground out to end the seventh, then began the eighth with an Alex Bregman groundout. His stuff was working, just as it had been all season.

Then, the misfortunes piled up. Kyle Tucker singled on a grounder that barely skipped into center field. Yuli Gurriel followed up with a weakly hit single. The Astros weren’t smoking the ball, but they had runners on first and second with one out. Montero needed a big pitch, and he got just that.

He just didn’t get the outcome he wanted.

Montero induced a potential double-play ball off the bat of Carlos Correa, which was hit right to Evan White. The Gold Glover fielded and fired over to second for the first out, but badly missed shortstop J.P. Crawford. The ball skipped into left field and Tucker easily scored, bringing the Astros within one run.

“It even happens to the best in the league every once in a while,” Servais said. “Errors happen; they’re part of the game.”

Seattle’s poor luck snowballed. Montero jammed Aledmys Díaz with an inside fastball, but Díaz muscled the pitch into center field for a bloop single to drive in Gurriel, notching the game up at five apiece. Montero walked Myles Straw, loading the bases, and his night was over.

Taking Montero’s place was Will Vest. Runner on every base. One out. Tie game. As solid as Vest has been, he could not keep the game knotted.

Vest walked Jason Castro with the bases loaded, giving the Astros a one-run lead. One batter later, Jose Altuve added an insurance run, knocking in Díaz with a sacrifice fly. Vest finished the inning, but the damage was done. For the first time this season, the bullpen imploded.

Montero may have gotten dinged with the loss and four runs (two unearned), but upon closer examination, he didn’t pitch that poorly; he just got unlucky.

Tucker had a seeing-eye single; Gurriel and Díaz’s hits had exit velocities under 80 mph; and, of course, White, one of the league’s best defensive first basemen, makes that throw more often than not.

“I didn’t think he threw the ball bad at all,” Servais said of Montero. “They got a few hits. That happens.”

Before the misfortunes of the eighth, the Mariners were shaping up for a feel-good win behind Dunn’s performance, one that featured both command and poise.

Dunn continued to exhibit growth, holding Houston’s hot hitting to three runs across 5 2/3 innings with two walks and two strikeouts.

Since allowing eight walks in his disastrous season opener, Dunn has only allowed five free bases in his last three starts combined. The raw stuff has always been there for Dunn, but the command is finally starting to come along, too.

“I like where I’m at,” Dunn said. “Definitely not going to be complacent and try to keep getting better.”

Along with minimizing the walks, Dunn managed to display some tranquility while under duress.

In the bottom of the fifth inning, Dunn allowed a one-out single to Straw and walked Martín Maldonado, putting runners on first and second with the top of the order coming up. Houston was one swing away from getting back in the ball game, but Dunn found an escape.

Dunn disposed of Altuve on one pitch, throwing a perfectly placed slider out of the zone to get the second baseman to fly out to center. Brantley wouldn’t be as aggressive, but Dunn went back to his breaking stuff and induced an easy groundout, ending the threat.

On most nights this season, Dunn’s performance would’ve been enough to net him a win. Just not tonight.

Bullpen blowups, as infuriating as they might be, are to be expected over the course of a full season. Now, it’s worth monitoring how the ’pen responds.