Every time the 76ers walk onto the court these days, they’re almost certainly without two of their best players in Joel Embiid and Paul George. Losing that type of talent can be too much for some teams to overcome.

For undermanned squads, their best comes from effort and aggressiveness. They must move quicker to loose balls, fight the hardest for rebounds, and work the hardest on defense. And maybe, just maybe, they can pull off an upset victory. In the Sixers’ case, a string of upset victories.

» READ MORE: Tyrese Maxey already has nine 40-point games. Only Allen Iverson had more for the Sixers by age 25.

But on Sunday night, doing those things didn’t end with a positive result. The Boston Celtics posted a come-from-behind 118-110 victory at the Wells Fargo Center. The outcome was the undermanned Sixers’ second straight loss after winning the previous four.

The Sixers (19-29) were doomed by 5-for-18 shooting, shabby defense, and a couple of costly turnovers in the fourth quarter. The Celtics made 68.2% of their shots — including 8 of 12 three-pointers — while outscoring the Sixers 38-16 in the decisive quarter. Four-time All-NBA selection Jayson Tatum scored 13 of his 35 points in the quarter while making 3 of 4 three-pointers.

“Well, I mean, the game the whole time boiled down to whether we could continue to get shots and score the ball,” said Sixers coach Nick Nurse. “The offense dried up. We played in transition a little bit. We kind of got forced into playing way more zone than we wanted to with Tyrese [Maxey] in early foul trouble and they hit, what eight threes in the fourth? … A lot of those they were missing [earlier in the game], but I don’t think we were getting quite out to contest.

“There were just too many point-blank wide-open ones and too many shooters out there … We were playing in transition a little too much defensively after not scoring the ball.”

While Tatum excelled, Sixers standout Maxey struggled in the fourth quarter. The point guard went 0-for-4 from the floor while scoring two of his 34 points. Maxey was frequently trapped in the final quarter.

“I didn’t do a good job of trusting it and trying to give the ball up early and let my teammates make the plays,” he said. “And then we didn’t do a good job, like our spacing. But that’s on me. I got to get guys in the right spot and kind of quarterback the situation.”

Guerschon Yabusele added 21 points in the loss.

But on this night, the Sixers had the edge in rebounding (46-38), points in the paint (42-34), second-chance points (10-5) and fast-break points (28-13).

The loss dropped them into a 1-1 season series tie with the defending NBA champion Celtics (35-15). They defeated the Eastern Conference’s second-place team, 118-114, on Christmas Day at TD Garden.

Back then, the Sixers were led by their Big Three of Maxey, Embiid, and George along with role player Caleb Martin.

» READ MORE: How much change is needed for a surging Sixers team before the trade deadline? It’s complicated.

However, Embiid (foot) missed his 15th consecutive game on Sunday; he last played on Jan. 4. The 2023 league MVP has played in only 13 games due to injuries and a three-game suspension. George (finger) has missed six of the last 10 games and 18 total because of injuries. And Sunday marked the 12th straight game and 17th overall that Martin (hip) has missed due to various injuries.

They weren’t the only sidelined Sixers.

Andre Drummond (toe), Eric Gordon (knee), KJ Martin (foot), and Jared McCain (knee) also missed the game. McCain will be sidelined for the remainder of the season after surgery. And for a while, it appeared that the sidelined players would not be missed.

The Sixers had a commanding 17-point halftime cushion. They extended their lead to 26 points in the third quarter.

As expected, the Celtics went on a run and took a 101-100 lead on Tatum’s three-pointer with 6 minutes, 51 seconds remaining in the fourth quarter. Luke Kornet’s dunk 31 seconds later gave them a three-point cushion.

“They were making those tough shots in the fourth quarter,” Yabusele said. “And they got going for like three, four, five possessions. … It was hard for us to contain them, and we didn’t find a great solution on offense.”