BOSTON — Jayson Tatum being sidelined with a ruptured Achilles may make the Celtics an easier opponent in theory, but the Knicks aren’t approaching a closeout Game 5 with that mindset. They are still treating the defending champions as if they are full strength, because like the Knicks had to learn to thrive with Jalen Brunson out for a month during the regular season, the Celtics, too, have experience competing at a high level with Tatum off the floor.

“[His injury] doesn’t impact how we prepare. We have to have the same mentality, same focus,” Brunson said after morning shootaround on Wednesday. “They’re still the defending champions. They still have championship pedigree. They still have a lot of weapons that are dangerous, so there can’t be a difference of how we approach it.”

Tatum has missed a total of 18 games over his last two seasons. The Celtics are 15-3 in those games and boasted an 8-2 record without their All-Star starter and franchise centerpiece leading into the 2025 NBA playoffs.

So what can we expect the Celtics to do in the absence of their star forward? For starters, recent history suggests Celtics head coach Joe Mazzulla will start Kristaps Porzingis instead of sixth man Payton Pritchard to compensate for the size Boston loses with Tatum (11.8 rebounds per game in Round 2 vs. Knicks) on the sidelines.

When the Celtics have had their full complement of players and Tatum is unavailable, Mazzulla has gone to the combination of Porzingis and Al Horford to keep the team’s positional size strong in the front court. Porzingis has been coming off the bench since he left Game 1 while dealing with a viral illness, but without Tatum, the Celtics will need both of their best bigs on the floor. They could also turn to Luke Kornet if they want to continue bringing Porzingis off the bench — but with the season on the line, Boston has little left to lose and will likely put its best available five players on the floor.

Without Tatum, Knicks defensive assignments will also have to change. OG Anunoby, for example, could shift to guarding Jaylen Brown, who will now be Boston’s top offensive weapon and has drawn the Mikal Bridges matchup for most of the series. Brown is averaging 20.5 points per game in the second round against the Knicks but has struggled to find any rhythm. He shot less than 38% from the field and 23% from three-point range through the first four games of the series.

But Anunoby, depending on who Boston inserts into the starting lineup, could also draw the Porzingis matchup, and the dual-big lineup for the Celtics will be formidable: five three-point shooters on the floor, including two who play most of their minutes at the center spot.

In games Tatum has missed due to injury this season, Pritchard averaged 19 points on 10 three-point attempts per game. He scored 43 against the Portland Trail Blazers, 34 in the season finale against the Charlotte Hornets, and posted 27 points and 10 assists in a victory over the Detroit Pistons. Porzingis only played in five of the 10 games Tatum missed this season but averaged 23.4 points, 8.4 rebounds and 2.2 blocks per game on better than 50% shooting from the field in those outings.

The Knicks will also need to do a better job of containing Derrick White, who hit six 3s and erupted for 23 in Game 5. White — who averaged 16.4 points during the regular season — appeared in eight of the 10 games Tatum missed this season. He upped his scoring to 20.8 points per game with the All-Star forward out of the rotation, averaging 11 three-point attempts with a bright green light without the All-Star forward.

PRAYERS OUT FOR TATUM

Brunson said the NBA won’t be the same with Tatum out for what will be an extensive rehab period.

“I feel for him. It’s an unfortunate situation for a player like him. The NBA needs Jayson Tatum,” he said Wednesday morning. “What he’s been able to do in his career has been remarkable, and he still has a long, long way to go in his — I mean, he still has a lot to do in his career. Meaning he has a lot of time left to make an impact for his legacy and what he’s done is special, so when you see a player like that go down, it’s just not good for the game.”

Mitchell Robinson, who returned to the Knicks rotation in late February after a 10-month injury layoff of his own, empathized with Tatum’s position,

“First off, I want to [send] prayers out to JT for that injury. I’ve been through a lot myself. I know how that feels,” he said. “It’s not a great feeling to be in. I mean, just to got to keep going.”

Tatum could miss the entire 2025-26 season recovering from the injury, as Kevin Durant suffered the same ruptured Achilles in the 2019 NBA Finals and missed the entire 2019-20 season with the Brooklyn Nets.

SPRING FILLED WITH UPSETS

The fourth-seeded Indiana Pacers upset the East’s No. 1 seed Cleveland Cavaliers completing a second-round gentleman’s sweep on Tuesday. The No. 3 Knicks walked onto the TD Garden floors with a 3-1 series lead over the defending champs on Wednesday. Out West, the No. 6 Minnesota Timberwolves pulled the upset on the No. 3 Los Angeles Lakers.

“Every playoff series is a battle no matter what,” said Brunson. “So that’s why you can’t — in your head — think about what’s going on with other series or anything like that. Yes, you’re aware of it, but you’ve gotta be focused on what you have to do because anything can happen.”

TUCKER’S INFLUENCE

Josh Hart shouted-out veteran forward P.J. Tucker for his influence on team culture since his late-season arrival. A reporter asked Brunson what Tucker has brought to the locker room during the playoff run.

“He’s brought a lot of shoes. He’s brought a lot of shoes,” he said of, Tucker, a well-documented sneaker head. “In all seriousness he’s been great. The way he talks, the way he leads. Obviously, he’s been around the league a long time and he has a lot  of experience and so when he talks we listen, so having a guy like that on our team has been remarkable for us. He’s been fantastic since he’s been there.”