PHILADELPHIA -- The fear of infamy can be a great motivating force.

Joe Mazzulla and Jayson Tatum felt this in different but important ways Thursday night as the Boston Celtics were facing a disastrous end to their season at the hands of the Philadelphia 76ers.

The young coach and the star player had to come face-to-face with the sort of lasting regret that ruins summers and sticks stubbornly on the résumé. They were left with no choice but to do something to avoid it, and that apprehension appears to have served them well as Boston stayed alive with a 95-86 Eastern Conference semifinal Game 6 victory.

It became clear that the bulk of the Celtics' roster had desired, behind the scenes, for the team to go back to the big lineup it rode to the NBA Finals last spring.

That meant Al Horford playing as the defensive center and Robert Williams III playing a prowling free safety, helping off the other team's worst shooter to roam and create havoc.

Last season, Williams dealt with a knee injury and was listed as a game-time decision often throughout the postseason (he missed seven games). He was so vital to the game plan that the nightly announcement often came with some measure of suspense.

But that so-called "double big" lineup, which crushed teams by 25 points for every 100 possessions together, was on the floor for a total of 81 minutes for the entire regular season and had yet to play a second in this series against Philadelphia entering Game 6.

Mazzulla, who was an assistant coach under Ime Udoka on last season's coaching staff, obviously preferred not to use it. He liked rotating Horford and Williams and using the extra spot for a scoring perimeter player like Derrick White or Malcolm Brogdon.

But Wednesday before they flew to Philadelphia, as he was getting skewered for his tactical moves in his first major series as head coach, Mazzulla relented. He told the players that, with James Harden getting into the paint too easily and Joel Embiid getting stronger by the game, that he'd go back to the old way.

Call it whatever you want: relenting, acquiescing or breaking; Mazzulla made a hard pivot and tossed his game plan away. And his players, after saying who knows what behind closed doors, loved him for it.

There was this:

"I was ecstatic about it," guard Marcus Smart said. "[Williams] is huge for us and I was proud to have him on the court and that just goes to show Joe's learning just like all of us. I know he's been killed a lot, rightfully so. He needs to make some adjustments and he did that and that's all you can ask for."

And this:

"I was excited," Horford said. "I'm pretty happy, Rob being out there. He just does so much for us defensively."

And this:

"It made a tremendous, tremendous difference and you could just see it," Jaylen Brown said. "It don't take a professional eye to see the difference that Rob made."

It worked. The 76ers started the game shooting 1-of-11, flummoxed by the Celtics' size and multiple possessions of zone defense that locked the paint down. Then down the stretch, the Celtics' defense stymied them again, forcing 11 straight misses in the fourth quarter as the game was put away.

The Sixers seemed unprepared as the lineup contributed to freezing their ball movement. Harden, who finished 4-of-16 shooting, and Embiid, who scored 26 points but was rendered ineffective in the fourth quarter, faded from a chance to advance to the conference finals for the first time in 22 years.

"I saw a sense of urgency, I saw a sense of togetherness," Mazzulla said. "The guys have shown that as long as they have played together."

Then there was Tatum, who was in a different mindset. His drama wasn't planned, he wallowed in it. After sitting around for a few days hearing about how he badly needed to get off to a good start for his team in an elimination game after going 0-of-8 out of the gate in Game 4 and 0-of-6 in Game 5, Tatum was playing one of the worst games of his life.

And it was ugly.

He was missing badly, making one of his first 14 shots. The Celtics, with their defense-first lineup, needed Tatum to pick up the scoring pace and at times he didn't even look like he wanted to shoot.

It had the makings of a dark day and no doubt social media, but less the non-digital commentary throughout New England, was all over him for it.

His teammates weren't watching TV or looking at their phones but they knew the backlash was permeating. One by one Smart, Brown, Horford, Brogdon, Grant Williams and more rotated to speak into Tatum's ear during timeouts trying to shake him out of it.

"That s--- was frustrating," Tatum said. "You want to win so bad, you want to play so well and shots not falling and things just not necessarily going away. And you want it, you want it so bad."

And you want to not face the wrath of failure. A day earlier, Tatum made first team All-NBA and it was well reported that made him eligible to sign a contract next year worth up to $318 million. Everyone saw that figure. And he was 1-of-14.

He kept looking at the game clock and telling himself there was time to do something. The score was tight and there was still room for a hero.

And Tatum saved the day. He scored 16 points in the fourth quarter, three more than the 76ers did as a team. He nailed 4-of-5 3-pointers. He stared at the crowd as they headed for the exits.

Then he walked over to do a walk-off interview in front of millions of fans with ESPN sideline reporter Cassidy Hubbarth and uttered an instant classic quote:

"I'm humbly, one of the best basketball players in the world."

Yeah, no infamy on this night.

"I truly believe that and I know that and it's easy to tell yourself that when you know you got 40 (points)," Tatum said an hour later after answering a flood of messages on his phone.

"But I think that shows character when you can tell yourself that when you've only hit one shot, when things not going your way, you know, got to be the same person, have the same morals, the same character up and down. And I just kept telling myself that I believe in myself until it turned around."