SEATTLE -- The September swoon in Seattle is manifesting into a full spiral, and the Mariners’ highly anticipated 10-game sprint to the finish against the teams they’re chasing in the American League postseason standings is nearing the point of disaster.

On the heels of a three-game weekend sweep in Arlington, Seattle was slowed in a 5-1 loss to Houston on Monday night to open its final homestand at T-Mobile Park. And with it, the Mariners are nearing a mathematically must-win outlook the rest of the way. Otherwise, their season will be over on Sunday.

• Games remaining (6): vs. HOU (2), vs. TEX (4)
• Standings update: The Mariners (84-72) fell to 4 games behind the Rangers (88-68) for first place in the AL West and to 1 1/2 games behind second-place Houston (86-71), which holds the third and final AL Wild Card spot. The Mariners are the first team on the outside looking in.
• Tiebreakers: Win vs. Houston (8-3); lose vs. Texas (1-8); likely win vs. Toronto (3-3, tiebreaker based on intradivision record).

“Really, a game at a time right now,” manager Scott Servais said. “You can't look any further ahead. We need to win tomorrow's game. That's just where we're at in our season.”

At times during the rainy, roof-enclosed night, it was challenging to decipher whether the boos that rained down were regularly scheduled programming for a Houston club that fans in this region loathe more than any, or toward the home team that manufactured just three hits and spoiled its only true run-scoring opportunity when the game was still within reach.

One certainty was that the loudest cheers of the night from the ticketed 39,920 echoed after the game was out of reach, when low-leverage reliever Dominic Leone hit Jose Altuve with a 96.3 mph fastball in the ninth. 

With the defeat, Seattle has now dropped 11 of its past 16 games, with three of its wins in this stretch to last-place Oakland.

“Terrible losses,” J.P. Crawford said. “All these losses suck right now, but there's nothing we could do about them. We’ve just got to keep our heads up.”

The Mariners fell on Monday at the hands of their longtime tormentor, Justin Verlander, whose statistical line was emblematic of his AL Cy Young Award seasons in 2019 and 2022 with Houston, but whose attack was far from it. Verlander thwarted Seattle with a bevy of breaking balls early in counts that either induced weak contact or led him to two strikes, at which point he dialed up his high-riding, four-seam fastball for strikeouts.

The likely first-ballot Hall of Famer flirted with his first shutout since his no-hitter in Toronto on Sept. 1, 2019, but a leadoff double in the ninth from Josh Rojas ended his night. Rojas then scored on a sacrifice fly from Julio Rodríguez, but it proved moot.

Verlander wound up needing just 96 pitches to go as far as he did, thanks to going 1-2-3 in seven of his eight innings. The lone hits he gave up were via consecutive singles in the third to Dominic Canzone and Rojas, followed by a walk to Crawford. That set up a moment begging for pandemonium -- Rodríguez in the batter’s box with the bases loaded -- but the Mariners’ best player hit into an inning-ending double play.

“We were just a big hit away from getting back into the game and momentum shifting,” Crawford said. “And after that, it's tough to get going with a pitcher like that.”

Verlander well outdueled Luis Castillo, who surrendered two homers, one triple and two doubles in what amounted to Seattle’s first loss behind “La Piedra” since July 30, snapping a stretch of 10 straight wins behind the ace.

Castillo came out firing with a 99.1 mph strikeout to Altuve to begin the game, then he came one strike away from working around a leadoff triple to José Abreu before the Astros ambushed him for three runs in the second -- all via fastballs, and all on line drives into the outfield gaps.

Castillo then surrendered solo homers to Yordan Alvarez in the third (on a slider well below the zone) and Kyle Tucker in the sixth (via a heater low-and-in).

“Today, I felt different,” Castillo said through an interpreter. “I felt healthy and amped. You can tell with the velocity going up a little bit. But it doesn’t matter how you feel, sometimes it doesn’t go your way.”

The Mariners’ postseason odds from FanGraphs have tumbled from 64.9% to 28% since the beginning of this final 10-game sprint. There were certainly tough-luck moments over the weekend, but Monday was another story.

“We got beat,” Servais said. “I mean, there’s no way around it.”

The Mariners have already been the first team on the outside looking in since Sept. 16, but the gap has widened and the schedule has shrunk. The long-awaited defining stretch of their season is finally here, and so far, it’s sending them toward an early exit.