The Boston Celtics had won 20 of 22 and brought a nine-game winning streak into their matchup against the Atlanta Hawks on Monday night. That streak certainly seemed safe when Boston's Al Horford hit a 3-pointer late in the second quarter to give the Celtics and 68-38 lead.

But the Hawks, clinging to the final play-in spot in the East and one of the league’s most disappointing teams, launched a comeback to top the Celtics, even with All-Star guard Trae Young and three other key players sidelined by injuries.

Dejounte Murray put the Hawks ahead to stay at 117-116 on a reverse layup with a minute left, and Celtics star Jaylen Brown missed a desperation 3 with the shot clock expiring.

What happened?

After the game, Celtics head coach Joe Mazzulla pointed out what went wrong for Boston, per Bobby Manning of CLNS:

Mazzulla points to managing runs & the margins. Said Celtics got good looks from 3 in the 2nd half, but Hawks physicality bothered the offense. Also noted that 58 times 20-point leads have been lost this year.”

The Celtics coach is correct on the Hawks getting through runs. Atlanta's comeback began with a 9-0 run to end the first half, which cut the deficit to 74-56 as the teams headed to the locker room. The momentum carried over to the third quarter, which began with Atlanta ripping off 19 of the next 23 points to slice the margin to 78-75.

The Celtics, despite 37 points from Jayson Tatum and 24 from Brown, struggled from the outside. Boston shot just 11-38 from the 3-point line on Monday night.

The Celtics' dominance this season

Despite blowing a massive lead to the Hawks, the Celtics have been the class of the NBA this season. At 57-15, Boston leads the second-place Milwaukee Bucks by an astounding 10.5 games in the Eastern Conference standings.

Having that type of distance in the standings has enabled the Celtics to avoid forcing players to play through nagging injuries – not only keeping players fresh, but giving their bench a reason to stay engaged this season.

The Celtics don't just have an elite starting lineup, led by Tatum and Brown but flanked with Kristaps Porzingis, Derrick White, and Jrue Holiday. Their reserves can come into the game and shoot the lights out while still playing withing Mazzulla's team concept.

It may seem counterintuitive, but if a team is consistently leading games by 30 points, then eventually their going to blow a 30 point lead. It's certainly not something that Celtics fans wanted to see as the team is looking to tune up for the postseason, but ultimately it does little harm in terms of where Boston stands.

The real key for the Celtics will be how they respond. Fortunately for them, they have a chance to get revenge on Thursday night when they take on the Hawks again. If Boston continues with their winning ways, then fans can look back at this tough loss on Monday night as nothing but a brief blip on the radar.