GREENBURGH — Folks kept calling Saturday’s game at Madison Square Garden the Knicks’ biggest at home in a quarter-century.

So what does that make Monday’s game? Bigger.

After the Celtics routed the Knicks, 115-93, in Game 3 of their Eastern Conference semifinal series — seemingly confirming the NBA world’s suspicions about how this series would go — it is up to the Knicks to wrest back the narrative and the momentum.

It will not be easy.

The Celtics trail 2-1 yet are favored to win Game 4 on the road and to win the series itself. It is a strange dynamic, but then, it has been a strange three games.

In all three, Boston has taken leads of at least 20 points in the second half. But only in the third did the Celtics finish the job, thanks mostly to a big improvement in their three-point shooting — from 25% in the first two games to 50% on Saturday.

Their 36.8% three-point shooting in the regular season is close to the middle of those two extremes. So let’s assume they settle into that range in Game 4.

Would that be enough to allow the Knicks to steal another win? To do so, they will need more from everyone than they got on Saturday.

Everyone undelivered, including OG Anunoby, who scored two points and  has only seven in his past two games. He scored 29 in Game 1.

Asked on Sunday what the Celtics are doing to throw Anunoby off his offensive game, coach Tom Thibodeau said, “The hard thing is we’ve got to get stops so we can get out in the open floor, create easy shots for each other.

“The first game, a lot was created off of the pace of the game, where we were able to create. He made six threes in that game, so he’s getting a lot of attention. He’s not getting the same room he had in the first game.”

Then there is Karl-Anthony Towns, who on Saturday shot 5-for-18 and might have broken a  finger on his left hand.

Thibodeau said on Sunday that Towns is fine. Josh Hart, the only player made available to reporters, also said, “He’s fine. It’s the playoffs, man. Everyone’s banged up. Everyone has nicks and bruises.”

As for Mitchell Robinson, his struggles from the free-throw line have emerged as a compelling subplot of the series.

He was 4-for-12 from the line on Saturday, including his second air ball in as many games.

On Sunday he posted a video on Instagram in which he said, “I know you’re all commenting and doing all the stupid stuff thinking that I really care. I really don’t.”

He said he  cares only about his truck, about playing basketball and about his daughter. He closed by sticking out his tongue and making an obscene hand gesture to the camera.

Strangest of all after Game 3 was the Knicks admitting that they did not play with the requisite “urgency.”

That was hard to figure, given the passion of fans, most of whom spent top dollar to be there.

Instead, it was a complete bust, with the Knicks trailing by as many as 31 points and many spectators leaving early.

It would be tempting for the Knicks to write it off as a bad day at the office, part of the normal ebb and flow of a playoff series.

But given the perceived ability gap between the Knicks and the defending NBA champions, Game 3 might be an ominous sign of things to come.

Fans seem to be having some doubts. As of late Sunday afternoon, tickets for Monday on the resale market could be had in the mid-$500 range, $200 to $300 less than before Game 3.

The Knicks are a bizarre 1-3 at home and 5-0 on the road in this year's playoffs. Dating to Game 7 of last season’s loss to the Pacers, they are 1-4 in their past five home playoff games.

Step One toward fixing it: Don’t trail by 20, because sometimes you can come back from that and sometimes you end up trailing by 31.

When a reporter from Boston on Sunday asked how the team deals with “clutch moments,” Hart responded, “The clutch moments? I don’t think there were many clutch moments last game.”

The Knicks hope to be ready for some in Game 4. It’s big.