Even with the postmodern realities about size and space in the NBA game, Boston Celtics coach Brad Stevens' shift toward featuring skill and speed has been remarkable.

Marcus Smart in the trenches defending centers six-plus inches taller and many pounds heavier than him? So be it. Playing at times with a point guard and four wings? So be it. Bucking the conventional wisdom they can't win big -- against rivals like the Philadelphia 76ers and their enormous lineup featuring Joel Embiid -- without getting more size? Maybe that, too.

It's been working. The Celtics are at the top of the East. Even while losing Gordon Hayward to a broken hand, Stevens has filled his lineups with shooters and unleashed an offense that ranks near the very top of the league.

Over the first month of the season Stevens has leaned into his roster and his preferred style of play, taking advantage of Kemba Walker's high-efficiency play and the defensive versatility and offensive talents of Hayward, Jayson Tatum, Jaylen Brown and Smart. The ball is moving, the players are working together and equal-opportunity offense is back after a little Kyrie Irving-involved hiatus.

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But it raises the question: Can the Celtics win in the postseason when they face some of the most talented big teams in the league?

What would they do with the Sixers and Embiid? How would they manage in a series against the Milwaukee Bucks or Toronto Raptors, both stacked with size?

Is this just an awesome regular-season story? Will that Embiid-sized hole in their lineup prevent a run to the Eastern Conference championship?

"We're just trying to play to our strengths. And our strengths are, without Gordon here, Marcus, Jaylen [Brown], Jayson [Tatum], Kemba, those are our best players," Stevens said. "So we're going to have them out a lot, and they'll be out a lot together. And when Gordon's back, all five of those guys, [there will] be four of them on the court a lot."

Kemba Walker has led the small-lineup Celtics to the top of the Eastern Conference. Nathaniel S. Butler/Getty Images

Stevens has long believed that, when in doubt, you should put your most mobile and versatile players on the floor. He didn't have to worry about size as much over the last few seasons because he had Al Horford, both mobile and big, in there. Before Horford arrived in 2016 for his three-year stint, though, Stevens experimented with players like Jonas Jerebko at center.

To manage it, he designed a defensive system where the players are asked to continually analyze the matchups and swap out size mismatches. It's a challenge in the heat of the game, but the Celtics have players who take on defensive challenges. Major competitors like Brown and Smart make this more feasible. The Celtics stand at sixth in defensive rating, making them the only team in the top six on both offense and defense.

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But then you go back and recall the season opener at Philly when the bruising Sixers outrebounded Boston 61-41 and won relatively easily. The Celtics double-teamed Embiid aggressively, and it limited his overall production, but that didn't change the outcome.

The Celtics are going with a committee at center. There's holdover Daniel Theis, rangy but undersized; newly signed Enes Kanter, who has size and is a good rebounder but a weak defender; and young Robert Williams, who is super athletic and can defend the rim but is inexperienced. All three have had injury issues. None of them makes anyone in Philadelphia worry.

But just a few days after losing to Philly, the Celtics beat the Bucks, tying them in rebounds, holding Giannis Antetokounmpo to a pedestrian 22 points and shutting down Brook Lopez.

"I think Milwaukee's a really interesting one, because if you're too big there, you're just too spread out," Stevens said. "So the more that you can be fast the better, but it's still easier said than done. And then Philly's size obviously was a big factor against us in Game 1, and we'll see how that goes throughout the course of the year."

The "we'll see how it goes" line might be the crux of the Celtics' season.

The reality is, the Celtics don't have easy options even if they were determined to upgrade in the middle. While one could have some fun with the Trade Machine, Boston has made it clear to anyone who has asked that their core players are absolutely not available. That includes, sources said, both Hayward and Smart, players who have been floated as possible trade chips in the past.

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Their best assets are as many as three first-round picks in the 2020 draft, including a valuable Memphis pick that is top-6 protected in 2020 and unprotected after that.

But finding a deal that works will be complicated in most scenarios by the need to send out equivalent salary without harming the team. Outside of their core five, only two players make more than $4 million: Theis and Kanter, who play the position Boston would be hoping to strengthen. Perhaps the Celtics can find a deal by the Feb. 6 trade deadline, but making a major move will be a challenge.

Stevens knows this, of course. The way he's developing this group shows it. Among his core beliefs is that if you can't handle an opposing player straight up, you have to figure out a way to change the nature of the matchup.

If the Celtics don't have a great answer for Embiid or Toronto's Marc Gasol, the answer is to make it just as hard for the opposing teams in other ways.

Scouts who have tracked the Celtics this season say Stevens has impressed with the way he's opened up his offense for Walker and the way he patches defensive holes by getting his guys to work together. But they also note the 76ers have one of the biggest rosters the league has ever seen and going small is an audacious play against it.

"Would I favor them in a playoff series right now against Philly or Milwaukee? Maybe not," one scout said. "You can focus on what they don't have, but if you look at what they do, you see they present you a lot of problems. Who knows what the matchups will be or who will be healthy in the end."

Indeed, ESPN's Basketball Power Index currently estimates that the Celtics and Sixers are only 28 percent likely to meet at any point in the postseason. For Boston and Milwaukee, the estimate is 44 percent. Even if those numbers rise a little, those matchups might never materialize for a variety of reasons.

Say whatever you want about the Boston coach -- his performance been a bit polarizing over the last couple of years -- but you cannot deny Stevens' creativity. His peers do not. At the end of Game 6 of the Finals last season, Golden State Warriors coach Steve Kerr drew up a brilliant play to get Steph Curry an open 3-pointer at the buzzer that would have won the game.

Curry missed it, and the Toronto Raptors charged the floor, but the misdirection design gave his team a great chance. Kerr had stolen the out-of-bounds play from Stevens.

This is Stevens' counter to the bigger contenders: run something creative and give it a chance. A month ago, most deemed the Celtics a second-tier contender. As Stevens' work with this reshaped roster and Hayward's outstanding play (before his hand injury) led the Celtics to the top of the standings, observers began hedging their preseason predictions.

The Celtics, after all that has happened to them, may have a real chance.

ESPN reporter Nick Friedell contributed to this report.