BOSTON -- Less than five minutes had passed in Friday night's final regular-season showdown between the top two teams in the Eastern Conference, the Cavaliers and the Celtics, and the game already felt over.

Cleveland coach Kenny Atkinson already had burned his second timeout, the Celtics already had made seven 3-pointers and Boston led 25-3, appearing well on its way to a massive statement win.

"We got punched in the mouth," Cavaliers star Donovan Mitchell said later. "What are we going to do about it? How are we going to respond?"

As it turned out, the Cavaliers responded rather splendidly. And it was thanks in large part to Mitchell, the six-time All-Star who finished with 41 points and five assists in 35 minutes in what eventually became a 123-116 Cavaliers victory at a sold-out and stunned TD Garden.

"I think they trust each other," Atkinson said. "They trust the message and they trust each other."

Entering Friday, the Cavaliers hadn't lost since falling to these same Celtics on Feb. 4 in Cleveland, a game that came less than 48 hours before the trade deadline. In response to Boston largely controlling that contest en route to a 112-105 victory, the Cavaliers went out and acquired De'Andre Hunter from the Atlanta Hawks for Caris LeVert and Georges Niang.

The move was designed to give Cleveland another big wing to throw at the likes of Jayson Tatum and Jaylen Brown. But by the time Hunter entered Friday's game, at the 7:11 mark of the first quarter, it looked like his minutes might only come in mop-up duty.

That quickly changed as the first quarter played out. Cleveland cut its deficit to 12 by the end of the quarter. And from there, it kept plugging away at Boston's lead thanks to multiple sustained runs led by Mitchell and a hot shooting night across the board. The Cavaliers finished 17-for-39 from 3-point range, with eight players hitting at least one from deep.

"It means we got grit," said Evan Mobley, who struggled for much of the game but finished with 17 points and 12 rebounds overall, including 11 and 8, respectively, in the fourth quarter. "No matter how down we get, we're going to keep fighting, we're going to keep going all the way to the end of the game, and tonight we kept fighting and they let us back in the game a few times."

The win erased any sliver of hope Boston (42-18) had of chasing down Cleveland (49-10) for the top seed in the East. The Cavaliers moved eight games up in the loss column with 23 to play and evened the season series at 2-2.

It also raised the specter of the Celtics' repeated issue of letting teams back into games.

And while Atkinson repeatedly pointed out that Boston was missing both Kristaps Porzingis (illness) and Jrue Holiday (finger), while Cleveland was fully healthy, the depth of the Cavaliers undoubtedly played a factor.

Cleveland used 10 players, with each seeing at least 12 minutes of action. Boston essentially played only seven, was outscored 33-6 in bench points (Payton Pritchard and Luke Kornet were minus-34 and minus-26, respectively) and was extraordinarily reliant on Tatum (46 points on 19-for-37 shooting, 16 rebounds, 9 assists) and Brown (37 points on 13-for-24 shooting).

"That was one of the most incredible shotmaking performances I've seen," Atkinson said of Tatum's performance.

Added Tatum: "Just being aggressive in a good rhythm. I think obviously the start of the game on defense ignited our offense and how we were playing. We did a really good job of what we were trying to do, and the actions and the spacing and we were trying to attack. And guys on both ends tonight were making shots. I think in the second half, they made a run in that third quarter, getting some offensive rebounds. They took more shots than we did, so that just kind of gave them some life. And in the moments that we needed to get a stop, we didn't, and that was tough."

As a result, Cleveland came away with a victory that instilled further confidence in a young, ascendant team a week after it throttled another potential playoff foe, the New York Knicks, at home.

And as both teams walked out of the Garden on Friday night, they already were thinking about what feels like a fated showdown in the Eastern Conference semifinals come late May.

"For sure," Darius Garland said when asked if it was meaningful that the Cavaliers had evened the season series, and how they did so, Friday night.

"It is 0-0. Hopefully, we'll be back here in the summertime, and we'll see it again for seven [more]."