The Celtics were ripe for the picking but the 76ers wasted a golden opportunity

Celtics forward Grant Williams stood his ground as 76ers center Joel Embiid looked to drive to the basket.Erin Clark/Globe Staff

If there was ever a night for the Philadelphia 76ers to exert their will against the rival Celtics, prove that their run of 14 wins in 18 games was no fluke, it was Wednesday night at TD Garden.

Not only did the Celtics shut down Al Horford and Robert Williams before the game with injuries, joining Marcus Smart on the inactive list, Jaylen Brown suffered a facial contusion in a collision with Jayson Tatum and left late in the first half.

That’s four starters out against a healthy 76ers team, but Philadelphia simply botched its chance to pounce on the vulnerable Eastern Conference leaders.

The Celtics’ 106-99 win says as much about Philadelphia’s ability to contend in the East as it does about Boston’s mettle. The Celtics led most of the game, withstood a late run, and won despite getting just 12 points from Tatum.

So what was Philly’s excuse? There wasn’t any. Approximately four months after Philadelphia walked into the Garden and got spanked on opening night, it happened again. It’s difficult to consider the 76ers real contenders when they looked uninterested in playing a complete game against a team that played hard and well.

Former Celtics coach Doc Rivers, who had apparently assembled a championship-worthy team, had no answers.

“We played flat the entire night,” he said. “We had wide-open shots all night but didn’t make them. But that can’t be a factor. I really didn’t think we played with the right spirit the entire night. I thought our defensive discipline the entire night was just poor.”

Rivers was right. Two glaring examples occurred in the fourth quarter when Malcolm Brogdon caught an inbound pass and drove around James Harden and Matisse Thybulle, who bumped into each other Three Stooges style, and Brogdon streaked in for a dunk.

Malcolm Brogdon made Philadelphia pay for dropping its guard on defense.Erin Clark/Globe Staff

Later, the Celtics had just a half-second to get off a shot. No problem, the 76ers ignored 7-foot Luke Kornet standing alone and he slammed home an alley-oop from Derrick White to extend the lead to 5.

The 76ers were lackadaisical most of the night, relying on the shot making of James Harden and an early surge from Joel Embiid, who scored 14 first-period points but just 14 more in the final three quarters.

Celtics veteran forward Blake Griffin was left completely alone several times and he burned his former coach with five 3-pointers, his most in a year. Griffin’s offense saved the Celtics in the early-going because neither Tatum nor Brown looked comfortable offensively.

“Blake Griffin hit like five or six threes and no disrespect but that can’t happen,” Harden said. “I think we did a solid job on (Tatum) but (Griffin’s threes) can’t happen.”

Besides Tatum, the Celtics shot 60 percent from the 3-point line, as Boston’s improved depth overwhelmed the 76ers. The Boston bench outscored Philadelphia’s, 41-21. Players such as Georges Niang and Tyrese Maxey got open looks and missed. The Philadelphia reserves provided no relief, turning the 76ers into a two-man brigade with Harden and Embiid.

The 76ers need more than that in the long run and Embiid realizes that.

“They went to the Finals and they have the best record in the league for a reason,” he said. “That’s a really good team. You look at tonight, Jayson didn’t have a good night but you’ve got other guys stepping up, knocking down threes. [Sam] Hauser coming off the bench, Brogdon giving them 19 or 20, Derrick White has been good the whole season and Grant Williams, he was great tonight.

“They’ve got a lot of options. And when you get to the playoffs, you need a bunch of guys like that, whether it’s create their own shot or make plays for each other.”

The Celtics whipped Philadelphia with teamwork and the 76ers have now slipped back into potential-pretender status. They had been chasing the Celtics for months, winning game after game preparing for this showdown, but they didn’t approach this game as significant. They lacked fire and passion. That’s disconcerting for Rivers.

“We didn’t score as a team tonight; we didn’t play offensively as a team,” Rivers said. “And then defensively, we were worse. I could have made those [Boston’s threes], well maybe not me but someone in this room could have made those threes. They were pretty much wide open. We gave up a lot of dare shots, all the way through the game.”

Rivers wasn't pleased with his team's performance Wednesday night against the Celtics.Charles Krupa/Associated Press

Philadelphia has some work to do. The 76ers need more depth. They can’t simply rely on Harden and Embiid. They need something out of Tobias Harris, who finished with 4 points in 32 minutes and continues to be one of the more underperforming players in the NBA. Even shorthanded, the Celtics exposed Philadelphia’s weaknesses and challenged their fortitude and toughness.

“Right now Boston has beaten us twice,” Rivers said. “Boston won the East last year. Boston is the best team in the East. It is our job to prove that wrong and we have a lot of time to do that.”