Eleven is the Yankees’ new magic number.

When Aroldis Chapman struck out an overmatched Albert Pujols to complete a 9-1 victory against the Angels on Thursday night in front of 42,056 at Yankee Stadium, the Yankees clinched the AL East and completed the initial leg of their quest for the organization’s first World Series title since 2009.

“This is the first step and hopefully we have a good run in us,’’ said Aaron Boone, who is the first manager in big league history to get 100 wins in each of his first two seasons.

In order to win the Fall Classic, the Yankees are going to need three victories in the ALDS and four each in the ALCS and World Series. So, in a lot of ways Thursday was the end of a six-month journey and the beginning of a short one that is stuffed with pressure.

“It’s important to realize how special this is and at the same time we have a lot of baseball left to play,’’ said Brett Gardner, who went 2-for-3 with a solo homer and a two-run double. “We have to continue to play good baseball and hope it is the beginning of something special.’’

The Yankees’ first AL East title since 2012 was followed by a low-key celebration on the field and the usual champagne and beer showers in the clubhouse. There was a down side to the night, however, because earlier in the day, 18-game winner Domingo German was placed on administrative leave by MLB due to a alleged domestic violence situation he was involved in Monday night.

So, after a season in which injuries — an MLB-record 30 Yankees went on the injured list — deleted big names from the active roster for long stretches of time, there is a chance German, who arguably is the Yankees’ most valuable pitcher because he can start and relieve, will miss the rest of the regular season, all of the postseason and could be suspended at the beginning of next year.

The win moved the Yankees to within a half-game of the idle Astros in the race for home-field advantage.

With scouts from potential postseason opponents — the Cardinals, Braves, Rays, Indians and Dodgers — on hand, Masahiro Tanaka (11-8) allowed one run and four hits in seven innings. Tanaka was 1-2 with a 4.82 ERA in his previous five starts, which included seven scoreless innings against the Mariners on Aug. 27. This was Tanaka’s first win since then.

DJ LeMahieu, a top AL MVP candidate, hit a three-run homer in the second inning. Cameron Maybin and Clint Frazier homered in the eighth inning. Didi Gregorius made three exceptional fielding plays, went 2-for-4 and stole a base.

Seven years without a division title for the Yankees seems like an eternity, but that was a topic heavily discussed in February when the wounds from getting waxed in last year’s ALDS by the blood rival Red Sox were still open.

“That was the goal in spring training. We got tired of playing in the wild-card game. To be able to accomplish that and win 100 games feels good,’’ said CC Sabathia, who is one of two players — Gardner is the other — left from the 2009 World Series champs and 2012 division winners. “Winning the division needs to be the goal every year. It’s been an incredible year. We got a long way to go and a lot of baseball left. Up to this point, had as much fun as any point in my career. We can deal with adversity, we’ve been through that. I think we are equipped to have a long playoff run.’’

Not lost on the Yankees was the fact that in the past two seasons, the Red Sox and Astros used division titles as springboards to hoisting World Series trophies.

“We saw how important winning the division was for the last two World Series champions,’’ said Aaron Judge, who didn’t play after making a diving catch Thursday night and landing on his right shoulder. “We were missing a lot of main pieces and [to] still win a division championship is special. Last couple of seasons in the playoffs we got booted a little earlier than we expected. We don’t forget.’’