BOSTON -- As the No. 8-seeded Miami Heat continue their torrid run through the Eastern Conference playoffs, coach Erik Spoelstra reiterated Thursday just how important he felt the regular season was in forming the mental toughness that has helped steer the Heat to within three games of another NBA Finals appearance.

In the midst of his description, Spoelstra made another important note regarding the NBA's play-in tournament.

"I do know the play-in helped," Spoelstra said Thursday. "There are far less teams tanking. Everyone was fighting for it those last two months. Every game was must-see TV and that was in both conferences. So I think [for] the league, that's probably the best thing that's happened in the last decade."

The Heat, who took a 1-0 lead over the Boston Celtics after a 123-116 Game 1 victory Wednesday night, became the first play-in team to ever win a playoff series after defeating the No. 1-seeded Milwaukee Bucks in the first round. The Los Angeles Lakers, who earned a spot in the Western Conference finals, became the second after knocking off the No. 2-seeded Memphis Grizzlies in the first round.

Spoelstra, who has been open about how much the up-and-down regular season helped prepare his team, said he believes that the Heat wouldn't be in this situation without going through all the struggles they endured.

"It was a blessing to be able to go through all of that," Spoelstra said. "I have not been part of a regular season like that, and I think we all grew and got better from it. To not let it collapse our spirit, but really to harden us, and steel us and bring us closer together and develop that kind of grit and perseverance that's needed in the postseason."

After compiling a 44-38 regular-season record, the Heat lost their first play-in game last month to the Atlanta Hawks before knocking off the Chicago Bulls two nights later to clinch the final playoff spot in the Eastern Conference. Both Spoelstra and his players have discussed how those experiences have shaped the group.

"If we didn't have those moments, those crushing last-second losses, and then also a bunch of guys being out all the time," Spoelstra said, "well, then maybe some of the guys that have contributed so much for us in the postseason, if they didn't have those opportunities where they had to score 20 points for us to win with Jimmy [Butler] or Bam [Adebayo] or whoever out, then they don't have that kind of confidence coming into the postseason. I really don't like that narrative that it only matters in the playoffs. I think we're a perfect example of the opposite of that."

Riding the hot hand of Butler, who has been arguably the most dominant player in this postseason, the Heat have displayed a consistency that was hard for them to maintain throughout the regular season. Now that the Heat have found a positive rhythm, Spoelstra credits the grind of the regular season for putting his team in a position to succeed.

"We are in that struggle fighting for our competitive lives for three straight months because of the play-in and because of all the adversity," Spoelstra said. "We were not doing the typical stuff of like load managing or just counting games; we were doing whatever we had to do to try and put ourselves in a position to win."

Veteran Heat guard Kyle Lowry agreed with the assessment while noting that the regular season is important "to kind of build your foundation."

Despite the fact that it appears the Heat have just turned it on over the past few weeks while racking up postseason wins, Lowry pointed back to the regular season as the training ground the Heat needed for bigger games.

"We've built our habits to know what we're gonna do and that's play hard every single night," Lowry said. "Be ready to go no matter what the situation is, who we're playing against, what we have out there lineups-wise. I think that's the one thing we did build through this year. The habits -- that we know that we can go and play anywhere with anyone at any time."

As frustrating as the regular season was at times for the Heat, Spoelstra said he would welcome the same kind of mental challenge again in the future.

"It seemed like every single game was going down to a last-second shot," Spoelstra said. "If you can be privileged enough to have a regular season like that all the time, that would be unbelievable."