The Boston Celtics’ elation after being selected as the top seed in the Eastern Conference were tempered on Monday night when they faced the Atlanta Hawks. The Celtics had a huge collapse in the third quarter to give up the lead, and they were outplayed in the final seconds to lose an incredible game, 120-118. The Celtics had led by as many as 30 points in the second quarter.

With 37 points while serving as the team’s nominal point guard, Jayson Tatum led the struggling Celtics. Although Jaylen Brown added 24 of his own, he had trouble being efficient for the most of the evening. With a combined scoring of 32, Kristaps Porzingis and Payton Pritchard completed the attacking focal points. All five of the Hawks’ starters—Dejounte Murray, Vit Krejci, Bogdan Bogdanovic, DeAndre Hunter, and Clint Capela—recorded double-digit scoring nights thanks to a balanced scoring approach, while Bruno Fernando added 13 points off the bench.

Although the Celtics have faced several shorthanded situations this season, the one they faced tonight was rather unusual. Coach Joe Mazzulla decided to play a starting lineup without any nominal guards in lieu of Derrick White, the current Eastern Conference Player of the Week, and Jrue Holiday, who had a dead arm. Instead, Tatum and Brown played as offensive initiators, challenging a Hawks starting lineup that included five players who were at least six feet tall: Al Horford and Sam Hauser. The unconventional starting lineup paid off right away as Tatum (14), Brown (13) and Porzingis (10) scored ten points or more in the first quarter, giving the Celtics a 44–22 advantage going into the second.

The assault persisted into the following frame. Before the quarter was halfway over, Tatum broke through for 20 points, giving the squad a 30-point advantage. The Hawks were just overpowered by the Celtics offense’s onslaught of points; they did not shoot especially poorly. But in the last moments, the Hawks managed a surge late in the half to get themselves within striking distance, portending more problems to come. At halftime, the lead stood at 74-56.

The teams’ fortunes drastically changed at the beginning of the second half. The Hawks ignited the State Farm Arena crowd with a 19-4 quarter-opening quarter against the Celtics, storming back to within three points of a lead in an utterly astounding comeback.

In the inevitable timeout that followed, Mazzulla said something, and it seemed to work. When the Celtics took the court again, they started out slowly and methodically, building an 8-0 run that completely destroyed the Hawks’ momentum. The unexpected hero of Atlanta answered, recording a personal 5-0 to bring the Hawks back to within a single digit. Although the Hawks managed to stave off the Celtics until the end of the quarter, the damage had already been done. This wasn’t the beginning of another incredible Hawks run. The Celtics were leading 96-90 going into the fourth quarter, and they were facing stiff opposition all the way to the finish line.

It didn’t take the Hawks long to finish the comeback. With a three-pointer from Wes Matthews, Atlanta immediately took the lead over the Celtics for the first time in the game, opening the fourth quarter with a 7-0 run in the first two minutes. After Svi Mykhailiuk countered with a three-pointer of his own, the Hawks swiftly reclaimed the lead. Thanks in part to a horrendous eight-second penalty from Tatum, Atlanta got out to a 15–5 start in the quarter and an unlikely four-point lead with eight minutes left in regulation.

For the following five minutes, the teams stayed very close to one another. With just under six minutes left, Boston tied Atlanta at 107 thanks to a string of timely baskets, including a surprising basket from rookie guard Jaden Springer. Following a Hawks timeout and two missed Murray free throws, Brown’s midrange jumper gave the Celtics the lead again.

As the clock ran out, the defenses started to make their presence felt, which worked in favor of the Celtics and their sly unit. With just over three minutes left, they were able to shut down the Hawks’ offense and pull up by four points thanks to a goaltending penalty against Capela. Quin Snyder, the coach of the Hawks, contested the ruling, and after a review, it was determined that the block was clean, removing the two Celtic points from the score.

In order to maintain a steady score as the game approached the final moments, Tatum made a midrange jumper and the teams exchanged free throws. With just under two minutes remaining, Capela missed a chance to tie the game, but Bogdanovic’s pull-up three-pointer gave Atlanta a one-point lead after the Celtics’ pointless trip. The Hawks’ 7-2 run over the following minute of play put them up 120-116 with nine seconds left, effectively ending the game. It was a shot that opened the door for them.

The Celtics will next remain in their current location when they take on the Hawks again this Thursday at 7:30 PM EST on NBC Sports Boston. The game will take place in Atlanta’s State Farm Arena.