SEATTLE — When Aaron Boone left the Coliseum in Oakland last week after the A’s took three straight from the Yankees, there was the usual calmness about him. His club’s lead in the AL East had been shaved to eight games and Boone showed zero concern that the sky could be falling.

His team was heading into Los Angeles for three games against the Dodgers, the two-time NL champion and a series being hyped as a World Series preview.

Maybe Boone knew the Yankees would take two out of three and beat Cy Young candidates Hyun-Jin Ryu and Clayton Kershaw in Hollywood before getting fat on the awful Mariners.

The Mariners are better than the Orioles, Tigers, Blue Jays and Royals, but nowhere near good. And certainly didn’t have the talent to hang with the Yankees on Tuesday night at T-Mobile Park, where the Yankees posted a 7-0 victory in front of 23,129.

So, after starting the nine-game West Coast trip 0-3, the Yankees have a chance to return home 5-4. Standing in the way is former Yankees pitching prospect Justus Sheffield, who was dealt this past offseason to the Mariners for James Paxton, who will start for the Yankees on Wednesday.

“It’s been nice to see,’’ Brett Gardner said of the Yankees bouncing back from being swept by the A’s. “Playing well says a lot about our team. We have done a good job of turning the page.’’

Masahiro Tanaka dominated the anemic Mariners lineup and won for the third time in his past four outings. Tanaka, who is 10-7, didn’t allow a run in seven innings and just three hits.

“First and foremost, the early runs helped out,’’ Tanaka said about Aaron Judge’s two-run homer in the first and Gardner’s three-run blast in the third. “As far as the pitching goes, better slider and good command of it. That was working for me.’’

Tanaka is the second pitcher in Yankees history to reach double-digit win totals in each of his first five major league seasons. Andy Pettitte did it in each of his first nine seasons.

Facing fellow Japanese pitcher Yusei Kikuchi for the first time, Tanaka continued his dominance of the Mariners. He is 8-0 with a 1.90 ERA in 10 career starts against Seattle.

Judge provided Tanaka with a 2-0 lead in the first inning when he homered to center off Kikuchi. It was measured at 462 feet and hit the batter’s eye on the fly. It was Judge’s 100th homer in his 371th career game. He is the third-fastest to 100 home runs in baseball history and has 17 this year.

“Just starting, I guess. Got to keep moving forward,’’ Judge said of reaching the milestone.

Gardner added a three-run homer off Kikuchi in the third, his 18th, and was impressed with Judge.

“When he puts the ball in play, it is hard to get in front of,’’ Gardner said. “When he is locked in, he is the best player on the field.’’

The win combined with the second-place Rays losing to the Astros hiked the Yankees’ AL East lead to 10½ lengths, which is tied for the season high.

When the Yankees get home, they have three games starting Friday with the A’s, who are in the thick of the AL wild-card race and will be armed with the confidence that they can beat the Yankees based on last week in Oakland.

What also happened in Oakland was the Yankees believing they were better than the team that lost three straight but has a chance to leave the West Coast with a 5-4 ledger after opening 0-3.

“Obviously a big game [Wednesday],’’ Judge said of the matinee that will determine whether they climbed all the way out of the 0-3 ditch.