BOSTON -- The list of bad losses this season for the Boston Celtics isn’t very long.
But the 129-120 overtime defeat to the Brooklyn Nets on Tuesday night?
Easily the worst of the bunch.
The Celtics led by as many as 21 points, entered the fourth quarter with a 17-point lead and were seemingly in cruise control all game.
And then it got close.
And with 0.2 seconds to play, Caris LeVert made a trio of free throws to force overtime as part of his monster 51-point performance.
Moments into the overtime session, the Celtics' Marcus Smart fouled out.
And then reality set in.
The Celtics and all their big-time scoring depth had nothing to show for itself in overtime.
Jayson Tatum (cold-like symptoms) did not play, Kemba Walker was on a minutes restriction after missing the previous five games with a sore left knee and was done for the game as well and Gordon Hayward had suffered a right knee bruise earlier and was unable to return.
The lineup Boston had on the floor in the OT session looked more like what you would expect to see in a preseason game.
But this game mattered, big time.
A win would have put them in a tie with Toronto for the second-best record in the East and it was there for the Celtics to take.
Here are more takeaways from a rough night at TD Garden:
51, way-too-easy points.
LeVert is a good player who can definitely score a ton, but the Celtics made it way too easy on him.
He got to wherever he wanted to with little to no resistance from anyone.
Smart is a first-team All-NBA defender, but the way he played on Tuesday … easily one of if not the worst game he has played defensively as a Celtic.
Smart is better than this; the Celtics as a team defensively are better than this.
The upside is that there are more than enough games left for them to brush this loss aside.
Still, if the season ends and they come up a game short of being where they want to be seeding-wise, all fingers will point to this game, one where the Celtics were at their absolute worst.
For the second game in a row, Smart had issues with the officials following a loss and there’s a decent chance that it’ll cost him a suspension this time.
He fouled out in the overtime session after having tallied his second double-double of the season with 14 points and 10 assists along with six rebounds.
For the most part, Smart had a decent game.
And they needed it with their top scorer (Tatum) out and their next-best scorer (Walker) playing limited minutes.
Still, this game will be remembered for his last-second foul he committed in the fourth quarter that ultimately forced overtime and having to be restrained as he went after the officials at the end of the game as the teams left the court.
His return to the Celtics lineup was definitely an adventure. He made mistakes, had some blown assignments and turnovers that proved costly.
Still, he also came up with some big rebounds in the fourth and made some timely free throws.
There’s no question he will be better going forward as the Celtics continue to gradually work him into the rotation.
For the game, he had 10 points while making all three of his shots from the field along with shooting 4-for-7 from the line to go with three rebounds.
Don't miss NBC Sports Boston's coverage of Celtics-Cavaliers, which begins Wednesday at 6:30 p.m. with Celtics Pregame Live, followed by tip-off at 7 p.m. You can also stream on the MyTeams App.