Trainers help the Celtics' Jayson Tatum off the court after he was...

Trainers help the Celtics' Jayson Tatum off the court after he was injured during the second half of Game 4 in the Eastern Conference Semifinals against the Knicks on Monday at Madison Square Garden. Credit: AP/Frank Franklin II

BOSTON — A single heartbreaking image said it all.

Jayson Tatum was caught by ESPN cameras screaming with his head in his hands as he was pushed in a wheelchair to the visitor’s locker room at Madison Square Garden on Monday night. Minutes earlier, the six-time Celtics All-Star had fallen to the court without contact with about three minutes left in what would end up a 121-113 Knicks victory over the defending champions.

Tatum’s injury is not the reason the Knicks head into TD Garden on Wednesday night up 3-1 in the best-of-seven Eastern Conference semifinal series. Rather, it is a cautionary tale for the Knicks — and all of the other aspiring champions left in the NBA playoffs — that painfully illustrates just how hard it is to get to the top of the mountain, let alone repeat.

On Tuesday, an MRI confirmed what almost everyone who saw Tatum writhing in pain suspected. He had suffered a ruptured right Achilles tendon and underwent surgery in Boston to repair it.

Though the Celtics said they expect him to make a full recovery, Achilles injuries generally take 12 months to fully rehabilitate. As a result, in Boston on Tuesday, they already were talking about the end of an era, about how this version of the Celtics dynasty suddenly is over before it could really begin.

Which brings us to the Knicks, who are one win away from advancing to the Eastern Conference finals for the first time since the 2000 playoffs. The Knicks have three chances to lock up that trip and beat the Tatum-less Celtics. Three chances to beat the team they were built to beat and move on.

The advice here, after watching Tatum’s and Boston’s repeat aspirations painfully crumble, is to get it done in one.

You have to have great players to win an NBA championship, but you also must have some great luck. Avoiding injuries is a big part of that luck in the NBA. Just ask Kenny Atkinson, whose Cleveland team charged out of the gate with 15 straight wins.

Cleveland, which was in first place in the East all season, has been dealing with injuries to Darius Garland, Evan Mobley and De’Andre Hunter in the postseason. All three missed the Cavaliers’ Game 2 loss to Indiana in Cleveland. Donovan Mitchell exited Game 4 early with an ankle injury, though the star guard started in Tuesday’s elimination loss to the Pacers in Game 5.

Or you could ask the Bucks, who lost Damian Lillard to an Achilles injury in Game 4 of their first-round series against Indiana and, as a result of losing that series, are likely to lose Giannis Antetokounmpo, who reportedly wants to be traded.

Or you could ask Golden State fans, who likely will witness the end of a dynasty Wednesday night when Golden State, down 3-1 to Minnesota, plays Game 5 without Steph Curry, who injured a hamstring in Game 1 of that series.

For all the grief Tom Thibodeau has taken for playing his starters heavy minutes, the Knicks have been relatively fortunate injury-wise. Yes, they lost Jalen Brunson to a bad ankle sprain for a month in the regular season, but Brunson is managing the pain in that ankle well enough to be averaging 30.1 points in 10 playoff games.

OG Anunoby appears to have some sort of hamstring issue. He left Game 4 Monday briefly, clutching his left hamstring, but returned feeling healthy enough to make some of the biggest buckets of the game, including a dunk on the play in which Tatum fell, clutching his Achilles.

Karl-Anthony Towns also appeared to suffer an undisclosed hand injury in Game 3 but has played through it.

All in all, the Knicks have been pretty lucky. But the more games you play, the more chances you have for your luck to run out, for a key player to get injured.

The Celtics still have enough guns to beat the Knicks without Tatum. Maybe not three times, but they can make things difficult.

The Knicks’ time to shine is now. They have a golden opportunity ahead of them and  would face the Pacers, a team they lost to in seven games last postseason, in the conference finals.

Since losing to the Pacers, the Knicks have become a stronger team, adding Towns and Mikal Bridges. And since entering the playoffs, a team that struggled to beat good teams in the regular season is playing its best and most exciting basketball.

The window of opportunity is now. And as anyone who watched Tatum being wheeled to the locker room Monday can tell you, those windows sadly don’t stay open long.

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