Will Ben Simmons play? And four other things to watch in the Celtics-Nets playoff series.

Jayson Tatum (left) scored 54 points in leading the Celtics past the Nets last month, 126-120, at TD Garden. Nets star Kevin Durant (center) poured in 37.Matthew J Lee/Globe staff

The last time the Nets came to TD Garden for a playoff game, the night ended with point guard Kyrie Irving stomping his foot on the face of Boston’s leprechaun mascot at midcourt before he walked to the locker room following his team’s Game 4 win.

The Celtics were overmatched in that opening-round series, which they lost in five games. Jaylen Brown missed all of it with a wrist injury and Kemba Walker was sidelined for the last two games because of a sore knee. Even before that, Boston was just a .500 team that needed to escape the play-in tournament just to get there.

But the mood for the rematch is quite different. James Harden plays for the 76ers now, and his replacement, Ben Simmons, has yet to play since being acquired in February. For Boston, Brown is healthy, Jayson Tatum is an MVP candidate, and the second-seeded Celtics spent the past few months throttling one opponent after another.

Boston won the regular-season series, 3-1. Irving and Kevin Durant sat out two of Boston’s wins, but in the Celtics’ 126-120 win March 6, though, the teams mostly resembled their current iterations, and Tatum erupted for 54 points and Durant committed seven turnovers.

“It’s a team and an organization that we know well,” Celtics coach Ime Udoka said. “And obviously playing them last year in the playoffs, [this time] will be different as far as overall personnel, but the head of the snake is [Durant and Irving].”

Here are some things to watch as Sunday’s opening game inches closer:

⋅ A Simmons debut?

Simmons remains out because of a back issue and has not played in a competitive basketball game since last postseason. It seems wild to think that he could instantly step into a high-intensity playoff game. But multiple reports indicate that the Nets remain confident that Simmons could make his debut at some point in this series.

What does the future hold for Ben Simmons?Matt Slocum/Associated Press

It could just be a ploy to disrupt the Celtics’ game plan, or it could just be wishful thinking. Even if Simmons comes back and plays 15-20 minutes a game, though, it would bring a substantial upgrade to a shoddy Brooklyn defense, with Simmons likely deployed on Tatum or Brown. Still, it would be asking a lot to expect Simmons to have instant chemistry with his new team.

“With Ben, you never really know from day to day whether he’s playing or not,” Celtics guard Derrick White said. “So when they say he’s playing, I’m sure the coaching staff will have a game plan for us. We’d kind of have to adjust on the fly for something that we haven’t really seen this year.”

⋅ The Alpha battle

The 33-year-old Durant is nine years older than Tatum, but the talent gap between them has narrowed to the point where it is no longer obvious which player is superior. Tatum’s 54-point explosion was the latest indicator.

The Celtics can probably overcome an average series from Tatum, but it’s unlikely that the Nets would be able to do the same with Durant. Tatum will be fresher and he has more weapons around him, but Durant is still more comfortable under the playoff spotlight.

“I guess not trying to make it a one-on-one thing,” Tatum said. “Obviously, everybody knows who Kevin is and the things he’s accomplished and what he brings to this game, but it’s a team sport. Obviously, he’s the focal point of their team and you’ve got to compete and game-plan and things like that to make it tough for him.”

Both players will have constant double-teams thrown their way. Tatum has improved as a passer and mostly handled these situations well this season. Durant can usually see above the traps and now has some willing shooters to spray the ball to.

⋅ Diverging defenses

The Nets own the league’s 20th-ranked defense and Boston sits in first. It was good for the Celtics to see last month that they can win a shootout against Brooklyn if needed, but they would prefer to muddy things up and punish the Nets with the physical, versatile, switch-heavy defenders.

The pesky Marcus Smart leads an elite Boston defense.John Tlumacki/Globe Staff

The greatest opportunities could come at the other end, where Brooklyn’s flaws are impossible to hide. Andre Drummond is still a good rebounder, but he is a below-average defender, and the Celtics have looked to punish him when he sags back in drop coverage. Irving sometimes ends up switched onto bigger opponents, and he often makes it appear that he is digging in before revealing that he is overmatched, giving up a basket, and shifting his focus back to scoring. The Celtics will look to isolate Irving and Drummond whenever there is a chance.

Udoka has often said that defense is his team’s best spark for offense, because missed shots ignite fast-break chances. The Nets are 25th in fast-break defense, so look for Boston to get out and run.

⋅ Return of Robert Williams?

Nets forward Bruce Brown created a bit of a stir Tuesday night when he basically said it was helpful that his team did not have to try to score against injured Celtics center Robert Williams, but Brown was not wrong. Williams, who is out after undergoing left meniscus surgery, emerged as a potential All-Defense pick this season. He averaged 2.2 blocks per game and made opponents reconsider a lot more shots than that.

Boston originally said that Williams would likely be sidelined for 4-6 weeks. Game 5 of this series would come exactly at the four-week mark. Williams has been completing two-a-day workouts and hasn’t suffered any setbacks and Udoka has left the door slightly ajar for Williams to return even sooner, although he offered a slightly more tempered view Wednesday.

“We’re happy with the progress, but at the same time, we understand it’s going to take time,” Udoka said. “And like I mentioned, probably be a full series about and that’s what we’re looking at doing.”

⋅ X-factors

Durant, Irving, Tatum and Brown should all have offensive eruptions at various times. But this series could ultimately be decided by more unexpected performances.

White struggled mightily from the 3-point line after being acquired from the Spurs in February but has made 55.6 percent of his attempts this month. Nets guard Seth Curry, meanwhile, has made 46.8 percent of his tries in 19 games with Brooklyn. One hot streak from a secondary source could shift the tenor of the series.