MIAMI -- Sunday morning, before the Celtics put their season on the line in Game 3 of the Eastern Conference finals, Jayson Tatum was asked why Boston has been so good away from home over the past two postseasons.

"We've had no other choice," Tatum said. "It was either win, or the season was over with."

Well, the Celtics didn't win Game 3. And, as a result, they find themselves staring down an 0-3 series deficit -- something 149 teams before them have failed to overcome.

After the Miami Heat obliterated the Celtics on Sunday night, leading by as many as 22 points in the first half and 33 in the game en route to a 128-102 victory, Tatum and the Celtics will have to summon something truly magical to turn this series around and prevent the eighth-seeded Heat from advancing.

"I don't even know where to start," Jaylen Brown said. "We can point fingers. But, in reality, it's just embarrassing."

Celtics coach Joe Mazzulla pointed fingers at one person: himself. In virtually every answer he gave, Mazzulla said some variation of the same thing: the loss was on him for his failure to have Boston ready for the biggest game of its season.

"I just didn't have them ready to play," Mazzulla said. "I have to get them in a better place to be ready to play, and that's on me."

Later, Mazzulla was asked whether Boston's defensive identity has been lost during these playoffs, as the Celtics went from being second in the league in defensive rating during the regular season to 10th in the playoffs, allowing 3 more points per 100 possessions in the postseason.

"Yeah, I think some of that defensive identity has been lost," Mazzulla said, "and we have to get that back."

Mazzulla's players defended him, with Brown saying it was a "collective effort," and Al Horford adding, "That falls on each player. We know what we have to do. We knew the magnitude of this game."

However the blame is assigned, what was impossible to argue was Boston laid an egg. The Celtics entered Sunday night 12-6 away from TD Garden over the past two postseasons -- far better than the 10-11 mark they've posted at home over the same span.

"I don't even know where to start. We can point fingers. But, in reality, it's just embarrassing."

Jaylen Brown

But like in Game 2, when Boston snapped what had been a streak of 16 consecutive wins for the home team after losing Game 1 of a series, the Celtics' history of road success didn't follow them south, either.

Unlike Game 2, which Boston controlled for large stretches, it was Miami that dominated the run of play in Game 3. The Heat, sensing an opportunity to press their advantage, closed the first quarter with a 16-6 run and never looked back, storming out to a lead of as many as 22 points in the second quarter.

Then, after Boston showed some life to get the deficit down to 15 at halftime and got an and-1 bucket from Marcus Smart to open the second half and make it a 12-point game, Miami immediately responded with a 22-7 run to stretch the lead back to 27 points midway through the third and push the Celtics to the brink of elimination.

"Tonight was tough," Tatum said. "From the beginning of the game, we were turning the ball over. We didn't shoot the ball well, they shot extremely well.

"It felt like we never recovered."

The Celtics entered this series as clear betting favorites to win an 18th championship after surviving a seven-game slugfest with their forever rivals, the Philadelphia 76ers, in the Eastern Conference semifinals. Now, just a week after Tatum scored 51 points and the Celtics hammered the 76ers at home to close out that series, Boston's season is all but over after a systematic annihilation at the hands of the Heat, who advanced out of the play-in tournament.

"As tough as tonight was, we just got to try to move on," Tatum said. "Prepare, get ready, practice, film and stuff for tomorrow. Obviously we're in a tough position. But we've got to have some pride, bounce back and just be better come Tuesday."

Virtually nothing went right. Boston has lived by the 3-point shot all season but hasn't made many in this series. After going 11-for-42 from deep in Game 3, the Celtics are now 31-for-106 (29.2%) from 3 in the series. Miami, on the other hand, shot 57% overall, 54% from 3 and is now shooting 44-for-92 (47.8%) for the series.

Mazzulla ditched Boston's two-big starting lineup of Horford and Robert Williams in the second half of Game 2, going back to the small grouping featuring Derrick White that he preferred much of the season. Mazzulla stuck with it to start Game 3. It didn't work, either.

A rough series continued for Brown, as he shot 6-for-17, had 12 points and was a game-worst minus-25. Brown is now 2-for-20 from 3-point range in the series. Tatum was hardly any better, going for 14 points on 6-for-18 shooting and was minus-23.

Neither was anyone else -- which is why Mazzulla had four of his five starters on the bench for the entire fourth quarter, instead having them watch the ongoing celebration carried out by the white-clad crowd at Miami's Kaseya Center.

"We're not out yet," Horford said. "It is 3-0. I know what it looks like.

"[But] we're not out yet. We're still kicking. One of four teams that are still kicking."