Three years ago, the Union went to Yankee Stadium on the last day of the regular season knowing they’d clinch their first home playoff game in seven years with a win.

Not only did they not get it, but they lost, 3-1, to New York City FC and fell to sixth place. That forced the Union to go back to the Bronx four days later, where they lost 3-1 again in the first round of the playoffs.

Just four of the players who were in the visitors’ locker room for those games are still with the Union: Alejandro Bedoya, Andre Blake, Jack Elliott, and Ilsinho. That is one of many measures of how much the team has changed since then, and for the better.

But one big thing hasn’t changed. The Union still have never won at Yankee Stadium, in what is now six trips. After a 1-1 tie in their first visit six years ago, there have been five straight losses — the most recent being a 4-2 loss in 2019 that was just as decisive as the 2018 matchups.

Here they go again, for another regular-season finale in the house that Derek Jeter built and David Villa made a home for MLS. Fortunately, the Union have already clinched a home playoff game this time. They can finish no worse than fourth.

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But the differences between second, third, and fourth place are stark.

Second lets you play another home game if you reach the second round.

Third sends you on the road somewhere else: either the NFL stadium that Nashville SC shares with the Titans, or back to Yankee Stadium again.

Fourth sends you to the Supporters’ Shield-winning New England Revolution, and Gillette Stadium’s artificial surface.

The Union will claim second place if they win, or if they tie and Nashville SC loses at home to the New York Red Bulls. If Nashville betters the Union’s result, it finishes second; if NYCFC wins and Nashville loses, the Pigeons finish second.

Had the Union not dropped seven points in 12 days against lowly Montreal, Minnesota, and Toronto FC, all these scenarios probably wouldn’t matter. The Union would likely have already clinched second place, and manager Jim Curtin would have fulfilled his long-held goal of Sunday’s game (3:30 p.m., PHL17) not mattering.

Alas, it matters quite a bit now.

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High-flying Pigeons

NYCFC is unbeaten in its last four games and has lost just once at Yankee Stadium since mid-June (with some home games moved to Red Bull Arena because of scheduling conflicts with the Yankees). Valentín Castellanos had five goals in his last three games and has a league-high 18 goals on the season.

And it’s not just the attack that’s been winning games. New York’s 35 goals allowed this season is the fourth-lowest total in the Eastern Conference.

“Their ability to counter-press and smother you and win the ball back as close to their goal as possible, they make teams make mistakes,” Curtin said. “They make teams uncomfortable, and then they have the quality to punish you and finish chances.”

It’s been two years since the Union last played in the Bronx, but Curtin hasn’t forgotten the history. Asked if it matters that his team has never won at Yankee Stadium, he didn’t hold back.

“It does,” he said. “You try to analyze the things that go wrong after games, and on that field, we’ve had two-goal leads evaporate, we’ve had situations where we’ve been down three goals and almost come back and won, 4-3. So there’s been wild, crazy games.”

It seems that the Union will stick with the 4-3-2-1 tactical setup they grew into over the last few games. They will do so in part because of that growth, and in part because Sergio Santos is likely out, and Cory Burke is likely to be available only as a second-half substitute. But Jamiro Monteiro is back at full health after missing last Sunday’s win over FC Cincinnati with a knee injury.

“You have now your two No. 10′s that can kind of almost, if you picture whatever side the ball’s on, one almost is out as a second striker and the other comes to that tip of the diamond and it looks like our 4-4-2, to be honest,” Curtin said.

“It doesn’t really change José [Andrés Martínez]’s job, it doesn’t really change Bedoya’s job, and it doesn’t really change Leon [Flach]’s job on the left side of the diamond — or [Jack] McGlynn, in the last game. They’re playing it like it’s a diamond in the formation, the same principles apply, the only thing that’s different is we have a second 10 in there, and hopefully that can clog the middle.”