BOSTON –  You realized the 76ers' trip to Beantown was close to being Mission Impossible when their chartered plane exited Philadelphia International Airport late Wednesday night.

That's because their best player, Joel Embiid,  and their heart and soul, T.J. McConnell, weren't on the trip. So the Boston Celtics, who boast the NBA's best record, were supposed to destroy the Sixers on Thursday night at the TD Garden.

They ended up winning, but it fell far short of being a massacre. In fact, the Celtics'108-97 victory was closer than the final margin would indicate.

Boston had to keep fighting off charges by its undermanned foe.

The Celtics finally got some breathing room on Al Horford's jumper that gave them a 103-90 lead with 1 minute, 25 seconds remaining.

"It's disappointing in a sense that when you battle and you play that hard and you lose, there's a little bit of soul searching there," JJ Redick said. "I think that's where it can be frustrating.

"But I'm proud of us. We fought and gave ourselves a chance to win a game in the fourth quarter. You have to give them a lot of credit for the plays they made down the stretch."

Celtics rookie  Jayson Tatum scored nine of his 15 points in the fourth quarter.  He made 4 of his 6 shots in the quarter.

Tatum and reserve forward Marcus Morris, a Philly native, teamed up on a 6-0 run that broke the game open for the final time. With Boston clinging to a 81-78 lead with 8:10 left, Morris scored on an 18-foot fadeaway. Tatum added a layup. Then Morris responded with a pair of foul shots to give the Celtics a 87-78 lead with 7:05 left.

"I think that he was the difference for us early in the fourth when we couldn't really score the ball," Horford said of Morris, who scored seven of his 17 points in the fourth quarter "He got us going."

Kyrie Irving scored nine of his 36 points.in the fourth. Horford finished with 21 points, eight rebounds and five assists.

The victory improved the Celtics to 19-4 and enabled them to win the first two of this season's four meetings in the series.  Meanwhile, the Sixers dropped to 12-9. It was their second loss in three games. They are also 1-2 without Embiid.

Ben Simmons, Redick, and Dario Saric kept them in the game on a night when Robert Covington continued to struggle.

Saric finished with 18 points and 10 rebounds. Redick added with 17 points while making 4 of 6 three-pointers.  Simmons had 15 points, seven assists, six rebounds five steals and five turnovers.  Meanwhile, Covington finished with 11 points on 4-of-13 shooting — including 3 of 10 on threes.  The small forward has made just  9 of 36 shots in his last three games, including 4 of 24 on three-pointers.

The Sixers could have used Embiid and McConnell.

Embiid has not been cleared to play on consecutive nights after left knee surgery in March. The center played 32 minutes in Wednesday's victory over the Washington Wizards. McConnell was sidelined with a sprained AC joint in his left shoulder. The backup point guard was hurt in the third quarter of Wednesday's matchup. An MRI exam Thursday morning showed no structural damage.

Reserve center Jahlil Okafor also didn't travel with the team. He and the team decided it was best to work out at the Sixers practice facility in Camden instead of traveling to Boston. That's because the Sixers did not have a morning shootaround that would have enabled him to work out.  Plus, he would have been listed as an inactive player for the game. So both sides decided it was best for him to remain home.

"We are trying to get him in a place where we can do whatever  we can help him to move his career forward," coach Brett Brown said.

The Sixers are looking to trade the third overall pick of the 2015 draft.

"When that moment, if that moment happens, we want to do everything we can to help him," Brown said. "He's genuinely good people. Everybody knows that."

Brown said it didn't know if the plan moving forward is to leave Okafor at home during road games.

To their credit, the undermanned Sixers kept battling. Down 10 points at intermission, they went on to take a 66-65 lead on Timothe Luwawu-Cabarrot's three-pointer with 3:56  remaining in the third.

The Celtics responded with a run and took a comfortable double-digit lead. However, the Sixers kept getting back into the game. But Horford's jumper with 1:25 left was too much to overcome.

This game was a homecoming for Amir Johnson (six points, six rebounds, three steals), who started at center in place of Embiid.  The 13th-year veteran played the last two seasons for the Celtics.