How the Boston Celtics Went from NBA Championship Favorites to Brink of Elimination

It was sitting right there for the Boston Celtics.

After the Milwaukee Bucks were upended in the first round by the eighth-seeded Miami Heat, Boston instantly became a clear betting favorite to win the championship.

Now five games into the Eastern Conference semifinals, and following a 115-103 beatdown at the hands of the Philadelphia 76ers on Tuesday (it wasn’t as close as the score suggests), Boston is one loss from elimination.

With the Celtics down 3-2 to reigning MVP Joel Embiid, FiveThirtyEight’s projection system now gives them just a 27 percent chance to return to the conference finals.

So, how did they get here?

Right now, it’s hard to look anywhere but the defensive side of the floor.

Last season, Boston allowed a whopping 5.1 fewer points per 100 possessions than the league average. This season, that mark was 3.3 points better than the average. However, among this year’s playoff participants, only the Atlanta Hawks, Phoenix Suns, Milwaukee Bucks and Los Angeles Clippers have given up more points per 100 possessions, per Cleaning the Glass.

And it’s often been the typically stout defensive backcourt that includes Marcus Smart, Derrick White and Malcolm Brogdon that’s been burned.

Trae Young got to at least 30 points in each of the last four games of that first-round series. Dejounte Murray had at least 23 in each of the first four.

With Embiid missing Game 1 of this second-round tilt against Philadelphia, Boston had an opportunity to open with a statement. Instead, it surrendered 45 to James Harden. Then, The Beard got 42 in Game 4. And though he only took eight shots on Tuesday, he picked the perimeter defense apart to the tune of 10 dimes. His backcourt mate, Tyrese Maxey, also dropped 30 points.

At the outset of a given pick-and-roll, isolation or whatever set puts someone like Smart or White against a creator up top, the containment hasn’t been as good as it was last season or even during the regular 2022-23 season. Jaylen Brown and Jayson Tatum haven’t been quite as menacing on the wings either.

But the bigger problem underlying all of that may be coach Joe Mazzulla’s unwillingness or inability (due to injuries) to deploy the two-big lineups that were so dominant in 2022-23.

Playing Al Horford and Robert Williams III together certainly limits Boston’s spacing. And you don’t think of twin towers as the best option against a heavy pick-and-roll attack like the one Philly used on Tuesday. But those two are mobile enough to survive on the perimeter. And more importantly, they make the back line more stout for the struggling guards and wings.

Tatum is a good defender, but he’s not the weakside menace that Williams can be.

Of course, that’s not the only reason Boston is faltering. The numbers are good on offense, but it’s not infallible either.

Brown is barely averaging more assists (3.5) than turnovers (3.1). After going 11-of-27 from the field in Tuesday’s loss, Tatum has been at or below 45 percent in seven of his 11 games. Horford is shooting below 40 percent from the field for the entire postseason.

But the biggest problem may be an overreliance on the three.

Boston’s 42.6 three-point attempts per game in the regular season trailed only the Golden State Warriors. And over the course of an 82-game campaign, that kind of volume is almost certainly a good thing. Bad nights here or there will be forgotten or replaced in our collective psyche by a season-long 37.7 three-point percentage that ranked sixth.

The postseason is a completely different ball game. It’s a pressure cooker. If you live and die by the three, the deaths feel a lot heavier. That weight can lead to pressure. That pressure can lead to thinking when you shoot. More misses. It’s a vicious circle.

Boston was 12-of-38 (31.6 percent) in the Game 5 loss. It’s now 1-4 in playoff games in which it fails to hit at least 39 percent of its triples. That’s a pretty high benchmark. But if the Celtics continue to defend this poorly, it appears that’s where they have to get.

Or, they have to find a way to take what defenses are giving them.

The desire to get threes up has become so ingrained in Boston that its players will often pass up good-to-great looks inside the three-point line for bad-to-OK ones outside it.

Suddenly, it feels like the Celtics need a borderline miraculous two-game stretch to get out of a series it was supposed to win handily.

But they still can’t be counted out.

They surged into that favorite position after the Bucks’ elimination for a reason. In theory, they check so many boxes. Williams, Horford and Grant Williams allow them to play big or small. They can get creation from several players on the roster, including Tatum, Brown, Brogdon, White and Smart.

And when engaged, the guards and wings are as versatile as any perimeter corps in the league.

That, of course, is the key.

Perhaps as much as any team left standing, the Celtics float in and out of focus for seemingly no reason. In what was the most important game of the season to this point, they looked completely disconnected on defense.

That can’t happen, especially against a team with two MVPs and plenty of shooting around them.

If Boston is going to make it to the next round, it can’t play with any complacency. It has to defend like the season is on the line (because now, of course, it is). It has to be willing to play big (literally and otherwise). And it has to be smart on offense.

That all sounds pretty obvious, but it’s the obvious stuff that the Celtics aren’t doing.