The Celtics closed out 2018 with a bad taste in their mouth.

Boston was dismantled in the third quarter, and it proved to be its downfall in a 120-111 loss to the San Antonio Spurs on Monday at AT&T Center.

Jaylen Brown led the Celtics with 30 points. Marcus Morris (18 points), Kyrie Irving (16), Terry Rozier (15), and Jayson Tatum (12) also tallied double figures for Boston. LaMarcus Aldridge had 32 points and was one of six Spurs in double figures.

With the loss, the Celtics fall to 21-15, while the Spurs climb to 21-17 with the win.

Here’s how it all went down.

STARTING FIVE

PG: Kyrie Irving

SG: Marcus Smart

SF: Jayson Tatum

PF: Marcus Morris Sr.

C: Al Horford

C’S CONTROL FIRST

Boston got off to a decent start and led 23-17 at the conclusion of the first period.

The Spurs took the lead right away by knocking down the first two points of the game, but that was the only time they led in the opening half. Boston used an 8-0 run over 2:07 just a few minutes into the game to take control, but their lead never got too comfortable in the opening 12 minutes. Most of the frame San Antonio spent within one or two possessions of the Celtics, even though they never could equalize or get back ahead.

Bryn Forbes led all players with eight first-quarter points. Brown paced the Celtics with seven.

CHAOTIC SECOND

Both sides posted 29 points in the second period, with the Celtics heading into the break up 52-46.

With a six-point lead in tow to begin the frame, the Celtics used a 12-2 run to open their advantage up to 11 by the 8:28 mark. The Spurs showed some impressive resolve later in the stanza while still trailing by 11, putting together a 9-0 run to cut the deficit to two with three minutes left. But in response, the Celtics outscored San Antonio 6-2 the rest of the frame.

Aldridge led the Spurs with 14 second-quarter points, while Brown had 11. Brown led all players with 18 points in the first half.

SPURS PUT FOOT ON GAS

Put simply, the Celtics got carved up in the third quarter. The Spurs outscored them 46-30 and took a 92-82 lead into the final frame.

The Celtics entered the period up by six, but a 16-0 run by the Spurs wiped that away. The run kicked off right at the midway point, with Aldridge finishing off an alley-oop at 5:59 to tie the game at 67 and get the spurt going. Aldridge had seven points over that 2:32 stretch, while DeMar DeRozan had five.

Although the Celtics started turning in some decent offensive possessions after getting dismantled, the Spurs answered enough to mostly keep their advantage hovering in the double digits.

Aldridge led all players with 12 points in the third, while Rozier had nine for the Celtics.

SPURS CLOSE DOOR

Although they outscored the Spurs 29-28 in the final 12 minutes, the Celtics never could make a strong enough run to really cut into the deficit, and it sealed the loss.

What befell the Celtics wasn’t so much offensive ineptitude, rather the Spurs answering on the offensive end seemingly every time the C’s got something going.

Kyrie Irving briefly left the game after taking a hand to what looked to be the eye. He returned and finished out the game.

Davis Bertans dropped nine points in the fourth.

PLAY OF THE GAME

This’ll make you dizzy.

UP NEXT

The Celtics will return home for a tilt with the Minnesota Timberwolves on Wednesday. Tip-off from TD Garden is set for 8 p.m. ET.