Instant analysis: Celtics avoid elimination by beating 76ers, force Game 7 back in Boston on Sunday

© Jim Davis/Globe Staff Celtics guard Marcus Smart was difficult for Joel Embiid and the 76ers to contain in the first half, scoring a team-high 15 points.

PHILADELPHIA — For much of Thursday night, it appeared that the Celtics’ season was on the brink and that star forward Jayson Tatum would be forced to shoulder most of the blame.

But after a miserable start in which he struggled, stumbled, and could do almost nothing right, he was there when his team needed him most, shaking off a 1-for-14 start by drilling three 3-pointers in a row to send the Celtics to a 95-86 win in Game 6 of this Eastern Conference semifinal series. Game 7 will be played in Boston on Sunday.

Tatum finished with 19 points on 5-of-21 shooting, but his late surge ensured that his night will be remembered in a positive light. Marcus Smart, meanwhile, was masterful for most of it, tallying 22 points, 7 rebounds, and 7 assists, helping the Celtics shake off an 18-turnover night.

Joel Embiid had 26 points and 10 rebounds to lead the 76ers, who were undone by 8-for-34 3-point shooting.

With the 76ers leading, 83-81, they started looking for home-run shots and missed a pair of tough 3-pointers before an Embiid jumper rattled out. At the other end, Tatum snapped out of his funk by hitting a 3-pointer from the left corner. On Boston’s next possession, he waved off a screen and hit another, giving the Celtics an 87-83 lead with 3:34 left.

Then, with the Celtics ahead by 5 and less than two minutes remaining, he calmly hit his third of the stretch, making it 92-84 and all but finishing off the win.

For the second year in a row the Celtics survived on the road in a Game 6 elimination matchup. Last year, they then returned home and walloped the Bucks in Game 7. Now, they will have to do it again.

Observations from the game:

· Celtics coach Joe Mazzulla altered his starting lineup a bit, putting Robert Williams in for Derrick White. The shift was done primarily for defensive reasons, and it had an impact at the start. Williams was assigned to P.J. Tucker, essentially giving him the freedom to roam as a kind of free safety. Tucker hit a 3-pointer early but missed his next three. And when 76ers guards reached the paint, Williams altered their shots or made them think twice about shooting in the first place.

Embiid also seemed aware of Williams’s presence. He tends to catch the ball about 15 feet from the hoop and fire up a jumper over Al Horford or look to attack. Embiid settled for jumpers most often with Williams on the floor. The 76ers opened the game 1 for 11 from the field, as the Celtics took a 13-3 lead.

Williams was even more impactful at the start of the third quarter, as the Celtics began to look for him roaming the baseline. He had one dunk and was fouled on another try inside.

· Tatum struggled through the first quarters of the last two losses before finding his rhythm later. But by that time the 76ers had found momentum and energy and the Celtics had to climb out of big deficits. His entire first half Thursday was miserable. He missed several open looks at the rim, did not draw a foul, missed all four of his 3-pointers, lost his footing on drives several times, and went 0 for 10 from the field. His only point came when the Celtics got a free throw after the 76ers were whistled for a transition take foul.

But nothing improved for Tatum in the third quarter. He finally got a runner to go to snap an 0-for-11 start. But then he missed a wide-open 3-pointer and had the ball knocked away inside. He also didn’t register a rebound or assist in the period. Early in the fourth, with the Celtics up by 1, Tatum had a 3-point look on a fast-break opportunity. He also could have attacked the rim. Instead, he hesitated, jumped, and threw a pass that was picked off.

It’s hard to consider a situation in which he should have been benched, but it was at least worth considering. Last season in this spot, down 3-2 on the road against the Bucks, Tatum erupted for 46 points in the biggest game of his career. Right now, he just seems off mentally.

· Unlike the last two losses, though, Tatum’s slow start in this game didn’t result in a double-digit deficit. The Celtics received much-needed shooting from the rest of their backcourt, as Smart, White, and Malcolm Brogdon combined to go 8 for 11 from the 3-point line in the first half. The Celtics led by as many as 16 points, but the 76ers sliced the deficit to 7 by halftime. It was hard to tell if the Celtics should feel great about having a lead after a no-show by Tatum, or terrified that they hadn’t truly capitalized on the dominant performance on the rest of their roster.

· With Robert Williams having an expanded role, forward Grant Williams, who has been deployed to guard Embiid throughout this series, did not play in the first half, as Mazzulla stuck with a seven-man rotation.

· The Celtics insisted that their best chance in this series would come by pushing the pace. That seemed particularly evident in the first half, when they held a 16-6 edge in fast-break points. Smart was usually the conductor.

· Boston’s perimeter defense at the point of attack was quite good. Robert Williams’s presence allows the backcourt players to guard more aggressively, and the Celtics did a good job of staying attached to James Harden while also taking away Embiid’s foul-line jumper that he had so much success with in Game 5.

· It seemed like the Celtics were getting the ball knocked away on every third-quarter drive. At the other end, P.J. Tucker was struggling to hit open looks so 76ers coach Doc Rivers subbed in Georges Niang, who hit a pair of 3-pointers and sparked a 12-point surge.