What to know about the Sixers vs. the Celtics in the NBA playoffs

Joel Embiid’s balky knee is the talk of Philadelphia ahead of a daunting second-round playoff matchup with Boston.

• 76ers head coach Doc Rivers said his star center is "doubtful" for tonight's game. He may have to wear a knee brace during the series.

Why it matters: Embiid is the key if the Sixers want to get one step closer to reaching the NBA Finals — something they haven’t done since 2001.

The intrigue: Wilt Chamberlain-Bill Russell. Dr. J and Larry Bird. Andrew Toney, aka “Boston Strangler.”

• The Sixers and the Celtics' killer rivalry stretches back decades.
• Tonight's tip-off is the 22nd time they'll meet in the playoffs — the most among two NBA teams, per ESPN.

Threat level: Boston won the last five playoff series between the two teams.

• This year, they beat us in three of the four regular-season games, with all decided by an average of less than six points.
• And we needed 52 points from Embiid in the only game we won.

Zoom in: Led by sharpshooting All-Stars Jayson Tatum and Jaylen Brown, the Celtics are favored to get back to the finals this year after losing to Golden State last season. The duo finished in the top 10 in scoring and can get hot at a moment’s notice.

💪 1 good thing: The Sixers have rested up for eight days, and Boston only had a weekend to recuperate after closing out the Atlanta Hawks.

💭 Isaac's thought bubble: Without Embiid, the Sixers can fuhgeddaboudit!