What was supposed to be an easy, momentum-boosting win before the Celtics embarked on a showdown with the NBA-best Milwaukee Bucks resulted in the latest disheartening performance in a recent string of setbacks against lowly teams.

The Detroit Pistons had just lost to the Cleveland Cavaliers, New Orleans Pelicans and Chicago Bulls, all at home. But the Pistons responded with an offensive masterpiece against an inept Celtics defense, handing Boston a stunning 116-103 loss at TD Garden Wednesday night.

The Pistons shot 60.3 percent against one of the league’s best defenses and dominated the second half. The Celtics looked overwhelmed and frustrated, unable to even run a clean fast break without an errant pass or missed layup.


Celtics coach Brad Stevens tried giving his front-line players a chance at rallying, despite a 16-point fourth-quarter deficit, but finally relented with just more than two minutes left. It was the Celtics’ most embarrassing loss of the season, considering Detroit is missing three starters, including All-Star Blake Griffin.

Derrick Rose, the former MVP, blasted the Celtics’ defense with 11-for-13 shooting and 22 points. Rookie Sekou Doumbouya scored 24 points on 10-for-13 shooting. Markieff Morris, mired in a major slump, scored 23 points in 22 minutes. The Pistons seemingly hit every open shot and every contested shots.

They were 35 for 46 on 2-point shots.

Even without Jayson Tatum, who sat out with a sore knee, the Celtics should have won this game handily. But once again they started slow and then allowed a game-deciding 15-2 run after they grinded to take a 71-67 lead.

Gordon Hayward finished with 25 points on 11-for-15 shooting and Jaylen Brown added 24. But the Celtics committed 15 turnovers, botched several chances at easy baskets off transition and could not get defensive stops. It was a frustrating night, especially for Marcus Smart, who was ejected with two minutes left after receiving his second technical foul.


Here are some observations from the game:

■  There were times the Celtics looked lost defensively, allowing the Pistons to pepper them with 2-point shots. After the quarters, Detroit was 27 for 34 on 2-pointers, as Doumbouya and Rose knocked down mid-range shots and layups. Svi Mykhailiuk came off the bench to hit four 3-pointers, including a 61-footer off the glass that gave the Pistons a 91-82 lead after the third period, leaving the TD Garden crowd restless.

■  The Celtics’ defense was a major issue in the first half as the Pistons were an eye-popping 17 for 19 on 2-point shots. Detroit shot 62.2 percent in the first half, led by 17 points from Morris in 12 minutes. The Celtics, frankly, were lucky to be leading at halftime but they did so thanks to 10 second-chance points and a 23-15 rebounding advantage.

■  Boston is a better team when Brad Wanamaker is scoring and he pitched in 7 first-half points, including a rare 3-pointer. After a sparkling November, Wanamaker has tailed off considerably. A pleasant surprise for the Celtics would be if he regains his previous form. Wanamaker had been 8 for 27 from the 3-point line since December before his second-quarter three.

■  It was a tough first half for potential Celtics trade target Andre Drummond, who took off his jersey after picking up his second foul in the opening quarter, apparently because he likes to change after each period. He finished with 4 points and five rebounds in 15 minutes but was saddled with three fouls. Drummond did not look engaged defensively.


■  Stevens said before the game he was unsure of the team’s plan for rookie Romeo Langford, who was expected to be sent to the G-League before coming down with an illness. Well, Stevens inserted Langford in the opening period for defense and he collected two rebounds and picked up a charge against Drummond. It’s obvious Stevens is comfortable using the 20-year-old Langford, but he just has to stay healthy.

■  The Celtics were uplifted by Hayward in the early going as they fell behind by as many as 9 points. Hayward has been erratic offensively since returning from his foot injury but he responded with six first-half field goals. He kept the Celtics close until Brown exploded for 17 points, 14 in the second quarter.

Gary Washburn can be reached at gwashburn@globe.com. Follow him on Twitter @GwashburnGlobe.