Brad Stevens has challenged the Boston Celtics to "get after it" as they bid to get back into their Eastern Conference Finals series against the Miami Heat.

Already up against a 3-1 deficit, it could be curtains for the Celtics' season on Friday when Game 5 comes around.

A regular-season record of 48-24, to Miami's 44-29, had indicated the Celtics should be competitive, while Boston also came out on top in two of their three previous clashes with the Heat in 2019-20.

Yet a 112-109 loss in Game 4 dealt a blow to hopes of reaching the championship series, with 20-year-old rookie Tyler Herro draining a career-high 37 points for Miami who are just a win away now from the NBA Finals.

"It's hard to win a playoff game, right?" head coach Stevens said.

"We're just looking at how can we play better on Friday night. That's the most important game of the season. We need to play our best game yet. That's it."

Coming from 3-1 down to win a best-of-seven series is a daunting challenge, but Stevens is not looking at the prospect of having to win three straight games.

The clear message from the coach is: one game at a time.

"I don't know what the historical odds are," he said. "It doesn't really matter. The situation we're in, we've got to play well Friday. We don't have to win three games on Friday; we have to win one.

"That's going to be our focus. That's going to be our attention. We'll get after it."