Doc Rivers faced a major challenge 10 years ago with the Celtics. He’s handled a similar one so far with the Sixers. | Mike Sielski

If there’s nothing harder in coaching than keeping the foundation of a championship team from cracking, Doc Rivers is 10 years removed from the sternest challenge of his 21-plus years in the profession, from the sort of situation that might inform his handling of Joel Embiid, Ben Simmons, and the 76ers’ sky-high aspirations this spring.

The Boston Celtics — with their “Big Three” of Kevin Garnett, Paul Pierce, and Ray Allen, with Rivers getting the trio to buy into a team-first mission right away — had come close to creating a mini-dynasty for a franchise full of big ones. They won a title in 2008, lost another in a seventh game to the Lakers in 2010, and won 56 games the following season before everything started falling apart.

In 2011, with Allen already having sacrificed shots and scoring to Garnett and Pierce through his first few seasons in Boston, Rivers wanted him to cede more playing time to Rajon Rondo. One year later, he even turned Allen into a sixth man during the 2012 playoffs so Rondo would have the ball in his hands more. The Celtics reached the Eastern Conference Finals and came within one game of beating LeBron James and the Heat, but come the summer, Allen was gone. Bitter over his diminished role in Boston, he signed a two-year free-agent contract with the Heat, winning another ring in 2013.

“I definitely thought Ray had to take the lesser role,” Rivers said Friday afternoon, with the Sixers up two games on the Wizards in the teams’ first-round series. “You do have to accept a role, everybody on the team, to win. You just do.”

That Rivers was able to squeeze that strong ’11-12 season out of that aging Celtics core — they struggled to beat the superstar-less Sixers in the conference semis — and with Allen so discontented is a testament to his ability to manage the personalities of the highest-profile players on his roster. A similar dynamic had threatened to hamper the Sixers, as long as Embiid and Simmons continued staging their subtle battle for supremacy, for the title of the team’s alpha dog.

That matter seems settled now. Embiid has established himself as the Sixers’ best and most vital player, a perennial MVP candidate if he can manage to play enough games. At the behest of the coaching staff, it has been Simmons who has made the sacrifice, embracing a role as a multifaceted facilitator, as a player who can rebound, distribute the ball, push the pace of the Sixers’ offense, and play great defense.

That’s the strategy that Rivers and the Sixers are employing here: Accentuate what Simmons does well. Double-down on it. Don’t demand that he get lost in his own head by asking him to shoot shots that he doesn’t want — or isn’t able — to take. In that context, of course Rivers is going to call Simmons a “treasure.” Of course he’s going to play up the positive aspects of every performance, even after a game in which Simmons fires up an oh-fer from the foul line. Rivers’ calculation is that, no matter the matchups and the floor-spacing and the opponent, a happier, more comfortable Simmons is the greatest of benefits to the Sixers.

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This is nothing more than the management of stars in the modern NBA, and this is nothing more than Rivers once again trying to find a role that an essential player will accept and thrive in.

“You just communicate it to them,” Rivers said. “Some guys can handle it. I thought Ray handled it for three years. He handled it just fine. When he became a free agent, I think there were a lot of other things at play. But as far as him taking that role, he did it for the good of the team, and all hats off. But everyone doesn’t have it. A lot of guys want to play the way they play, no matter what. In my opinion, that eventually doesn’t work. If everybody on every team got to play the exact same way that they only wanted to play, I don’t know if you can win that way. It’s tough.

“Part of winning is being a team that sacrifices. But you always learn from all those different experiences. Everybody’s different. Everybody handles things differently. Some need overcommunication. Some don’t need any. You wing it every year with your group. You really do. Just got to have a feel for it.”

A coach also has to have credibility with his players, and Rivers’ championship with the Celtics and his own 13-year NBA playing career afford him that. They are advantages and accomplishments that his predecessor, Brett Brown, simply didn’t have. “I think all those boxes are checked with Doc,” forward Tobias Harris said. “He’s done a great job with this whole group of getting us to realize how to play for one another and how to handle our business and limit our distractions. On the personal side, you just realize that if we win, that takes care of all the business there.”

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It always does. It did in Boston, and it will here. Under Rivers, Harris has seen his play and production improve, seen himself become a bona fide third centerpiece player in the lineup, and this series against the Wizards isn’t likely to test the Sixers in any meaningful way. But those tests are coming, for Joel Embiid, for Ben Simmons, and for the coach charged with repeating the trick he pulled off all those years ago: winning it all before it all starts to fall apart.