Boston Celtics forward Jayson Tatum (0) shoots against Miami Heat forward Jae Crowder (99) during the second half of an NBA game Tuesday, Aug. 4, 2020, in Lake Buena Vista, Fla. Kim Klement/Pool Photo via AP

From general manager Elton Brand’s preseason mandate he expected the 76ers to “win big” to coach Brett Brown’s confidence his roster was suited for a deep playoff run, the championship outlook was high in Philadelphia.

Philadelphia 76ers’ Joel Embiid (21) celebrates from the bench during an NBA game against the Houston Rockets on Friday, Aug. 14, 2020, in Lake Buena Vista, Fla. AP Photo/Ashley Landis, Pool

Look at the 76ers now.

All-Star guard Ben Simmons is out indefinitely after left knee surgery and All-Star center Joel Embiid has a banged-up right hand and sore left knee. Al Horford was benched for a spell and underachieved in his first season on the 76ers.

That added up to a mediocre 42-30 finish and the sixth seed in the Eastern Conference, far below what the Sixers expected at the outset.

After two straight trips to the East semifinals, the Sixers are the betting underdog when the series opens against the Boston Celtics (48-24).

Game 1 is Monday.

This postseason could surely be Brown’s last stand in Philly after seven seasons if the Sixers can’t survive the injuries and often-mismatched roster to make a deep postseason run. His public optimism high, Brown believed there’s something left in the 76ers — even without Simmons.

“I believe we are built for the playoffs,” Brown said. “We’ve been beaten up. Now is our moment. Now is our time to be recognized.”

For all his faults, losing a defensive stopper in Simmons was a massive blow for an organization that has never put it all together under Brown’s watch. Simmons averaged 16.4 points, 8.0 assists and 7.8 rebounds this season, and his 35.4 minutes per game led the 76ers.

“There’s a different path than there used to be with Ben but there is a path,” Brown said.

Embiid missed one game with a sore left knee and hurt his right hand this week but played 22 minutes and scored 14 points in the finale on Friday.

“We clearly need a healthy Joel Embiid,” Brown said. “Nobody denies that. We can’t dismiss that.”

The Celtics are ready to pounce.

BOSTON BELIEVES

A year after Kyrie Irving’s injury-riddled and disruptive two-year tenure ended in Boston, coach Brad Stevens said the Celtics are in a much better place than the team that lost 4-1 to the Bucks in the second round of the playoffs last season.

“Obviously, last year was really difficult, but I think this year has been reinvigorating in a ton of ways for a ton of us,” Stevens said. “And I think that we’re all excited about where we are and where we’re headed.”

The Celtics’ fortunes this postseason will hinge on the play of their young core, namely Jayson Tatum.

“They have so much firepower. They really can score,” Brown said. “They have four players that can get 30 on a given night. I feel like their ability to put points on the board, their ability to create shots is just lethal. Our ability to defend those types of things ultimately will tell the story.”

Tatum hasn’t lost any of the momentum he had before the hiatus. A first-time All-Star this season, Tatum ended the seeding games averaging a team-high 23.4 points. He’s also shooting 45% from the field and 40.3% from beyond the arc.

Tatum liked the Celtics’ improvement during the bubble.

“Obviously we continue to get better. And I think we have from Game 1 being down here to now,” he said. “I think we keep getting better each and every game and I think that’s what you want at this time of year.”

WALKER’S STATUS

Kemba Walker, who tweaked his left knee during a workout before the team arrived in Florida, has been slowly working his way back to full strength.

The All-Star point guard started off slowly in the bubble but posted his best effort of the seeding games in Tuesday’s win over Memphis, scoring 19 points on 7-of-10 shooting from the field.

More importantly, Walker said he felt as confident on his knee as he’s been since the injury.

“It’s getting there,” Walker said. “I was as comfortable making my moves and stuff like that. It was good to make that move and see the ball go in as well. I’m working every single day to get my leg stronger and my knee stronger. I’m feeling good. Hopefully I can continue to feel good and I’ll just continue to take care of myself.