MIAMI >> Maybe Kevin Garnett was right. Maybe, as he screamed in celebration of Boston’s 2008 NBA championship, anything truly is possible.

Even the impossible.

The Celtics are halfway to history, and that alone has gotten them entry into a very small club. Of the first 150 teams that trailed a best-of-seven series 3-0 in NBA history, just 14 — 9.3% — found a way to extend the matchup to Game 6. None of them have won the series, and most are usually eliminated by now.

Not the Celtics. They have cut the deficit in the Eastern Conference finals against the Miami Heat to 3-2, simultaneously trailing the series yet seeming to have all the momentum going into Game 6 in Miami tonight.

“Obviously, we didn’t imagine being in this position, being down 3-0, but when adversity hits, you get to see like what a team is really made of,” Celtics forward Jaylen Brown said. “I mean, it couldn’t get no worse than being down 3-0, but we didn’t look around, we didn’t go in separate directions. We stayed together. We doubled down on what we’re good at on defense, and now I think it’s a series.”

Only three teams have gone from down 3-0 to tied 3-3; the Celtics could be the fourth with a win today. No NBA team has ever fully escaped the 3-0 hole, but a win today would give Boston a chance to change that in Game 7 — which would be Monday on its home floor.

“One of our assistants put it in great perspective: The seasons are like nine months long, and we just had a bad week,” Celtics coach Joe Mazzulla said. “Sometimes you have a bad week at work. We obviously didn’t pick the best time to have a bad week, but we did, and we’re sticking together and fighting like hell to keep it alive.”

Meanwhile, the Denver Nuggets are waiting for an opponent. If Boston wins the series, the Nuggets will visit the Celtics for Game 1 of the NBA Finals. If Miami wins the East, the Heat are headed to Denver for Game 1. Either way, the title series starts June 1, somewhere.

“We have to shore up who we are and address the areas that we have not been maybe good enough or areas that we can clean up,” Nuggets coach Michael Malone said Friday, after the team’s first real practice since sweeping the Los Angeles Lakers for the Western Conference title. “But it’s really hard to keep your rhythm when you’re not playing NBA games.”

The Heat had a nine-point lead in the third quarter of Game 4, in position to perhaps win in a sweep. The lead was gone 2-1/2 minutes later and the Celtics haven’t trailed since. An 18-0 run in Game 4 put Boston on top of that game for good, a 12-0 run by the Celtics later in that game ended all doubt, and then they started Game 5 with a 20-5 burst.

Add that all up, and from the start of the third-quarter run in Game 4 to the end of the start-of-game spurt in Game 5, the Celtics outscored the Heat 84-43 in a span of 27 minutes.

“The last two games are not who we are. It just happened to be that way,” Heat forward Jimmy Butler said. “We stopped playing defense halfway because we didn’t make shots that we want to make. But that’s easily correctable. You just have to come out and play harder from the jump. Like I always say, it’s going to be all smiles and we are going to keep it very, very, very consistent, knowing that we are going to win next game.”

At least the confidence isn’t ailing. Everything else is.

Heat coach Erik Spoelstra flatly shot down the notion that Miami has an excuse for the way it played in Game 5 — “there’s no excuses. Not at all,” he insisted — even though the training room is as crowded as a scrum for a loose ball under a basket right now. The Heat have been shorthanded in the backcourt for the entirety of the playoffs after injuries to shooting guards Tyler Herro and Victor Oladipo, plus they didn’t have starting guard Gabe Vincent for Game 5 and watched Kyle Lowry play through some sort of hand issue.

Miami’s starters were outscored 95-44 in Game 5, and since the start of Boston’s comeback-sparking burst in Game 4 the Heat have been outscored 75-33 from 3-point range, allowed the Celtics to shoot 54% from the field, 44% from 3-point range while committing 26 turnovers to Boston’s 12.

Pick a number. They’re all bad for the Heat, except the one that matters most — 3-2, the series score that means Miami is still only one win from capping its own improbable run of being a No. 8 seed that found its way into the NBA Finals.

“It’s a competitive series,” Spoelstra said. “You always expect things to be challenging in the conference finals. One game doesn’t lead to the next game. … We beat them by whatever in Game 3. It just doesn’t matter. It’s about collectively preparing and putting together a great game. We’ll play much better today. That’s all we just have to focus on right now.”