SEATTLE -- The curious case of Rafael Montero continued for the Mariners and their bullpen alignment after another tough outing that contributed to a 4-1 loss to Oakland on Friday at T-Mobile Park.

The stakes were as high as they’ve been all season -- given the Mariners’ standing in the postseason hunt and against the very team ahead of them -- but the landing spot figured to be soft. Montero came on in the eighth inning with Oakland clinging to a one-run lead despite 13 strikeouts from a brilliant Sean Manaea, and his matchup featured the Nos. 7-9 hitters: Matt Chapman, Seth Brown and Elvis Andrus, who entered the night hitting a combined .219 and were 1-for-6 entering the inning.

Yet, Montero worked himself into a bases-loaded jam and wound up surrendering two runs against seven batters.

On a night when runs for both teams were incredibly tough to come by, that sequence proved to be the dagger. And it put a damper on the Mariners opening arguably their most critical homestand since embarking on their multiyear rebuild following the 2018 season.

“You can't pitch the same guys every night,” manager Scott Servais said. “They all have to pitch in your bullpen. Monty needed to pitch. There was a spot for him. We were down in the ballgame. We really thought it was, ‘Bottom of the order, hopefully get him through it, and then give us a chance to get back in and pick up another run.’ But it’s tough to win a game when you only score one run.”

More than anything, it’s when traffic mounts that Montero gets in trouble, which was again the case Thursday.

Montero by leverage, 2021, entering Thursday:
High: .314/.395/.514, 3 HR, 5 2B, 10 K, 6 BB, 81 PAs
Medium: .409/.480/.500, 0 HR, 2 2B, 4 K, 3 BB, 25 PAs
Low: .262/.308/.357, 1 HR, 5 2B, 23 K, 5 BB, 91 PA

Chapman’s single bounced on the infield and wasn’t cleanly corralled by reigning Gold Glove Award winner, shortstop J.P. Crawford, which put Montero into an immediate hole. From there, things spiraled in an eerily familiar -- albeit not as drastic -- way they did when he blew a three-run lead with two outs and two strikes on June 12 in Cleveland.

“Rafi hasn't been as sharp here for quite some time,” Servais said. “Part of it is just, [Chapman], he leads off the inning, gets into a deep count, has a little nibbler that J.P. tries a short [snag on]. That starts off the inning, and then a soft hit after that, then you look up and the bases are loaded.”

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As has been the case in past outings that Montero has stumbled, it was a spot the Mariners were hoping he could work through and build upon -- and one that was likely mapped out well before game time.

Lefty specialist Anthony Misiewicz would’ve been slated for the heart of the order featuring two lefties, Matt Olson and Mitch Moreland, had Montero gotten away with little or no damage allowed. Paul Sewald and/or Kendall Graveman, both of whom were on one day’s rest, would’ve been called on in the ninth had the Mariners kept things close.

Given that Chris Flexen was chased with one out in the sixth despite an otherwise solid showing, the Mariners had to turn to JT Chargois sooner than they would’ve liked to escape that jam. Additionally, Drew Steckenrider needed 31 pitches to navigate through a scoreless seventh. That left only Montero or Erik Swanson, who threw 15 pitches on Wednesday in Denver, for the critical eighth-inning sequence.

“All of our guys have got to pitch, and kind of where we're at, I thought it was a good spot to get him in there. And he certainly needed it,” Servais said.

All season, the Mariners have highlighted that, despite tangible results that have led to a 7.27 ERA, Montero’s stuff is among the very best on the entire pitching staff, starter or reliever. They’ve also pointed out that underlying metrics suggest he’s been a victim of poor luck -- his xERA, which takes into account the amount and quality of contact, was just 3.50 entering Thursday, while his exit velocity readings are way down.

But the Mariners have now lost each of the past seven games that Montero has pitched in dating back to June 27. He has a 12.60 ERA and has given up 22 hits to 56 batters in that stretch. One single reliever can’t be pinned for each of those losses, but for a team teetering on contention -- and for a bullpen that has been the club’s biggest catalyst -- leverage sequences such as Thursday’s loom large, especially with eight days to shape the trajectory of Seattle’s Trade Deadline strategy and the scope of its second half.