After the Celtics’ regular season concluded last week, Kristaps Porzingis snapped a photo of the TV inside the players’ lounge at the Auerbach Center. There was an important message on the screen.

“0-0,” it said.

The Celtics won 64 games this season – the fourth most in team history – as they dominated the NBA. They secured the top seed in the East by a preposterous 14 games as they boasted the best offense in league history.

None of it matters now.

The Celtics, at last, start the playoffs Sunday, and nothing short of a championship will be a justifiable result for this group. All the pieces are in place, and everything is set up for them to bring home their first title in 16 years.

Their first opponent in their quest? Of course, it’s the Miami Heat.

Five things to watch as the first round begins:

1. The Porzingis effect

Porzingis was back home in Latvia at this time last year watching the NBA playoffs. But he wasn’t totally enjoying it. He wanted to be part of it.

“I’m thinking to myself like, ‘Of course it’s nice to finish the season early, but there’s nothing else to do,’ ” Porzingis recalled recently. “What is there better to do than to play basketball? Nothing.”

Porzingis will finally get his wish. The 28-year-old has been in just 10 career playoff games, and never made it out of the first round. But after a blockbuster trade to Boston last summer, he is now central to the Celtics’ championship hopes.

Porzingis played in just 57 games as the Celtics managed his health to be peaking right now. When he did play, his performances were everything they looked for and more on both ends of the court. His acquisition was, in some ways, a reaction to their loss to the Heat in last season’s Eastern Conference Finals, as the Celtics looked for more answers against opposing defenses. Now, it’s time to prove it.

“Playing in the postseason is going to be incredible. I’m looking forward to that,” Porzingis said. “Of course it’s going to be hard, it’s going to be tough physically and mentally. But if we want to achieve what we want to achieve, then it’s not going to be easy.”

2. An emotional hurdle

Heat star Jimmy Butler will miss this series after suffering an MCL injury in their play-in game loss to the 76ers this week. But that doesn’t mean the Celtics should overlook their opponent.

Celtics fans will rightfully have some PTSD when the Heat walk into TD Garden on Sunday afternoon, and the C’s should be plenty motivated by the sight of them. The Heat, of course, ended the Celtics’ season less than 11 months ago with that brutal Game 7 loss in the Eastern Conference Finals.

The Heat might not have the same firepower without Butler, and even though they had another underwhelming regular season, their championship-level DNA remains with Erik Spoelstra at the top. Bam Adebayo, Tyler Herro are dangerous, and Caleb Martin – as the Celtics learned last spring – can get hot quickly. Maybe this is the opponent the Celtics need to set the tone for their championship run.

3. The turnover battle

The Celtics don’t need to look any further than Game 7 last season to know the importance of securing the ball against the Heat. They committed 15 turnovers – including eight from Jaylen Brown, who had the ball in his hands more after Jayson Tatum left injured – in that season-ending loss.

Without Butler, the Heat’s defense may not be as impactful, but it remains a part of their DNA. The Celtics committed the fewest turnovers per game in the league this season, but facing the Heat can be a different story.

4. Clutch time

The Celtics set an NBA record this season with 17 wins by 25 or more points. They outscored their opponents by an average of 11.34 points per game, which ranks as the fifth best in league history. Their talent is so good that it’s easy for them to blow teams out, and there will likely be several lopsided victories in the playoffs, but one area of concern that has persisted is their ability to win close games.

The C’s were certainly better in the clutch this season, but there were several losses – the Cavs and Nuggets defeats included – where their worst flaws under pressure came to light. Their offense slows down, and they struggle on final possessions. In their pursuit of a title, they’ll have to win a few close games, and that could come in the first round against a Heat team that had 22 wins in the clutch this season, tied for the eighth most.

5. Taking care of business

Another test for the Celtics this season? Don’t make it harder on yourselves.

The Celtics, of course, made their road harder than it had to be last season. They had to go six games against the Hawks in the first round after dropping a Game 5 clincher at home. They had to battle back from a 3-2 series deficit to defeat the 76ers in the second round. The extra work caught up to them when they tried and failed to overcome a 3-0 series deficit to the Heat.

The C’s have been blessed with a favorable road as the No. 1 seed in a vulnerable East, and they need to take advantage. Get some extra rest, and be at their best for the NBA Finals if they can get there.