LAKE BUENA VISTA, Fla. -- The Boston Celtics were 0.5 seconds away from taking a commanding 3-0 lead in their Eastern Conference semifinal series against the defending champion Toronto Raptors.

But after Raptors forward OG Anunoby shook free for a stunning buzzer-beating 3-pointer that saw Toronto escape with a heart-stopping 104-103 victory, Celtics forward Jaylen Brown didn't attempt to hide his disgust over allowing the Raptors to survive -- and remain in the series as a result.

"That was just a f---ing disgrace at the end of the game," Brown said. "That was just terrible.

"No way we should have lost that game. I take responsibility for that. Not just that play, but a lot of the plays before. And it happens. This is the NBA playoffs. Either you let them gain momentum or you come back and be ready to play next game."

It looked like the Celtics had all but ended Toronto's quest to defend its title after Kemba Walker made a ridiculous play to split a double-team by Raptors guard Fred VanVleet and center Marc Gasol, get into the lane and throw a no-look bounce pass to Daniel Theis for a dunk with 0.5 seconds left to give the Celtics a 103-101 lead.

But as Toronto attempted to inbound the ball -- with 7-foot-5 Tacko Fall, having subbed in for Walker, defending the inbounds pass against Kyle Lowry, who is listed at 6 feet -- there was a miscommunication between Jayson Tatum and Brown as Anunoby ran along the baseline to the opposite corner of the basket.

Tatum thought he had alerted Brown to stay with Anunoby and wound up going to double-team VanVleet. Brown, meanwhile, had stayed with Gasol just long enough in the paint that as Lowry's pass sailed over everyone to Anunoby, who was waiting in the corner for it to arrive, he had to try to fly out to defend it.

But he managed to get there only after the ball left Anunoby's hands -- leaving him, and the rest of the Celtics, helpless to do anything but watch the shot fall through the net as the buzzer sounded. Boston's players threw their hands in the air in disgust while Toronto's players did the same in celebration of saving their season.

"Just a miscommunication [of] the coverage that we were in," Brown said. "That's all that really is. They made a remarkable play at the end. [Anunoby] snuck along the baseline, and we just gotta communicate better, that's it. As a unit, that can't happen. We were matched up, and OG snuck along the baseline, didn't recognize him early enough and he got a wide-open look.

"We gotta be better than that. We gotta communicate better. Me being four years in, I gotta be better. Can't give up the 3 at the end of the game. ... He made a remarkable shot, but still.

"It's a f---ing disgrace. Terrible. No excuse for it. At all. It was ridiculous. Can't take your foot off the gas at all. We gotta be ready to play Game 4."

After Boston blew out Toronto in Game 1, the past two games have played out like most expected before the series began, with two of the best defensive teams in the NBA grinding out games that have come down to the final seconds.

In Game 2, it was Walker who hit the biggest shots of the game in the final two minutes to seal the win. In Game 3, it was Walker who made the absurd pass to Theis to seemingly do so again.

"That was a great play," Brown said. "He did his job, he drew two and found the open man. He put us up two. It was a big play for us.

"Point-five on the clock. We just needed one stop to win the f---ing game."

But the Celtics didn't get that stop. And, in the span of that half-second, they saw their chance to put a stranglehold on this series slip away -- and allow the defending champions to have a new lease on life.

"I mean, they're a really good team that we're playing against," Celtics coach Brad Stevens said. "They're tough, smart, they put you on your heels. But I thought our guys really competed, really fought.

"Both teams left it all out there tonight in a great game. It hurts and it stings to lose, but we'll just get back to it and get ready for Saturday."