BOSTON — There was no way to know how the Sixers were going to respond to a six-day layover between closing out Miami and playing Game 1 against the Celtics in Boston. A defensive collapse is what happened.

"I thought it was one of our poorer defensive games that we've played in a while," coach Brett Brown said.

The rust vs. rest pros and cons were discussed all week, and shortly before tipoff there was a bit of an indication from Brown that the rest might not have been a good thing for his team.

"Time off isn't always the answer to playing well," Brown said with some uncertainty.

There still is no way to really know if it was rust that hampered the Sixers on Monday. One thing is for sure — the Sixers have plenty to review and ponder following the 117-101 Game 1 beating they took from the Celtics. And, once again, the Sixers will have some extra time off to make their adjustments.

"I don't know if the time off hurt us," Brown said after the game. "It sure felt like we were playing a good team today."

With Game 2 slated for Thursday night, both teams will have two full days to make any changes and clean up problem areas.

Chiefly among the things the Sixers will need to address is the way the Celtics exposed the defensive limitations of Marco Belinelli and JJ Redick.

Robert Covington, usually the team's defensive specialist, also had a rough night, which was more unusual, but it certainly added to the Sixers' woes.

The Celtics were searching for any way to get a switch onto Belinelli and take advantage. One such instance came with just over seven minutes left in the second quarter when Shane Larkin, coming over the top of a screen, found himself guarded by Joel Embiid. That meant that right next to them, Belinelli was tasked with guarding Al Horford. It didn't end well for Belinelli.

Redick spent most of his time chasing Jayson Tatum without much success. Tatum beat Redick with a multitude of moves — running downhill, on step-backs, pump-fakes, and with his handles. Tatum went off for 28 points.

"We will look at that," Brown said of the coverage tasked to Redick.

When it wasn't Tatum going off, Terry Rozier was using his athleticism to beat the Sixers. Often shooting over Belinelli or blowing past him. Rozier finished with a team-high 29 points for the Celtics.

"It starts on defense," Embiid said. "I thought we were all bad. That's not who we are."

Jaylen Brown (hamstring) is expected to return for the Celtics on Thursday, giving them yet another explosive scorer.

The Sixers will have to make adjustments, be more diligent reacting to mismatches and getting back to their man after a switch, and hope they can find enough offensive production to make up for their defensive lapses, should they happen again.