SEATTLE — A challenging schedule awaited the Mets as they departed Queens late Sunday afternoon, and two games into that slate, all is hardly well.

Tuesday night a combination of underwhelming pitching, ugly defense and mediocre offensive output sank the Mets in an 8-3 loss to the Mariners at T-Mobile Park. The Mets lost their second straight game to begin the road trip.

Gone are the positive vibes that accompanied the Mets to the Pacific Northwest after a weekend sweep of the Marlins that extended their winning streak to four games.

The Mariners, who won their eighth straight, are a legitimate threat to win the AL West and the Mets will continue this West Coast swing in San Diego against a Padres team very much in the NL playoff mix.

“Baseball, especially right now, there’s so much talent from so many good teams — you can sweep a team and then you can get swept,” Mark Vientos said. “But our job is to prevent that as much as possible and just get on a streak and stay hot.”

Vientos had a rough night defensively, committing an error at first base that led to a run in the fourth before misplaying another ball that was ruled a single in the fifth, helping to extend the inning before Jhonny Pereda hit a three-run homer.

How would Vientos evaluate his season defensively?

“Pretty good,” he said. “I have done a pretty good job over there. I have been working.”

Jonah Tong had his first rough outing in three appearances since his recall from Triple-A Syracuse. The right-hander surrendered five runs, four earned, on five hits and two walks over 3 ¹/₃ innings in a bulk relief role.

Overall, the Mets surrendered three homers on a night the Mariners built a comfortable cushion by the fifth inning and rolled to the finish. The Mets will try to avoid a series sweep on Wednesday with Freddy Peralta on the mound.

“We have got to start playing better,” manager Carlos Mendoza said. “Until we start playing consistent baseball, that is the only way to get out of it.”

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Among the few Mets’ positives was rookie Carson Benge, who blasted two home runs to continue his recent offensive outbreak. But the Mets were hardly dynamic offensively, a night after getting only two hits in a 3-2 loss in 10 innings.

Huascar Brazoban, who served as the opener, worked into the second inning. Dominic Canzone singled with one out before Brazoban got ahead 0-2 in the count to Patrick Wisdom and left a changeup over the plate. Wisdom crushed it for a two-run homer that gave the Mariners a 2-0 lead. Colt Emerson doubled to end Brazoban’s night before Tong recorded the inning’s final out.

Benge unloaded for a two-run homer in the third that tied it 2-2. A.J. Ewing doubled in the inning before Benge delivered with two outs against Logan Gilbert. Leading off the game, Benge took Gilbert to an 11th pitch before striking out.

Two fielding blunders by the Mets led to an unearned run for the Mariners in the third. After Marcus Semien misplayed Randy Arozarena’s line drive into a two-base error — his throw to first base was errant, allowing Arozarena to reach second — Vientos mishandled Luke Raley’s soft liner. Arozarena scored on Vientos’ error, giving the Mariners a 3-2 lead.

“There have been stretches where we have been playing well defensively,” Mendoza said. “And then there’s been stretches where we are making errors on routine plays.”

Tong walked J.P. Crawford to load the bases in the fourth before Julio Rodriguez’s sacrifice fly extended the Mets’ deficit to 4-2. Tong retired Arozarena to avoid further damage. Wisdom’s walk and Pereda’s single started the rally.

Pereda delivered a gut punch with a three-run homer in the fifth that gave the Mariners a 7-2 lead. The rally started with Young’s grounder off Vientos’ glove — ruled a single — before Canzone singled. With two outs, Tong threw a cutter on his ninth pitch to Pereda that disappeared behind the fence in left-center.

Benge’s second homer of the night closed the gap to 7-3. The multi-homer game was the first of Benge’s career.

Cionel Perez surrendered a homer to Rodriguez leading off the bottom of the frame to give the Mariners an 8-3 lead.

A.J. Minter, in his first back-to-back outing since returning from his minor league rehab assignment, worked a scoreless eighth inning. A night earlier Minter surrendered the game-winning hit in the 10th inning.