Whoever wins the second-round series between the Philadelphia 76ers and Boston Celtics is going to be heavily favored to represent the Eastern Conference in the Finals. The Sixers squandered a golden chance to close out the Celtics on their home floor Thursday night, and now this back-and-forth tussle is headed back to Boston for a massive Game 7 on Sunday.
Here are four factors that will determine which East juggernaut is able to advance to play Miami.
Boston's big adjustment, Philly's potential counter
The biggest overarching tactical shift in Game 6 was the Celtics reverting to last year's double-big starting lineup, slotting Robert Williams III in at center and bumping Al Horford down to the four. The two had shared the court for just seven minutes in the series up to that point.
Williams, who played an enormous role in Boston's 2022 Finals run but has been hampered by knee issues, averaged only 18.1 minutes per game through the first five games of this series. In Game 6 he played 27, and his team needed every one of them. The Celtics were a plus-18 in those minutes, and a minus-nine in 21 minutes with Williams on the bench.
On offense, he provided the kind of roll gravity and above-the-rim finishing the Celtics otherwise lack. On defense, Boston kept Horford on Joel Embiid and stuck Williams on P.J. Tucker so he could play free safety and short-circuit Philly's actions at every turn. In 19 minutes with both him and Horford on court, the Celtics held the Sixers to a miniscule 80 offensive rating.
The Sixers eventually realized they could diminish the defensive impact of the two-big look by yanking Tucker and forcing Williams to defend a legitimate offensive threat, rather than allowing him to rove to his heart's content. Swapping Tucker out for Georges Niang early in the third quarter confronted the Celtics with a difficult choice. They could have Williams continue to defend a wing, but in this case one who could shoot, which would make it much less tenable for him to help at the rim; or they could move him onto Embiid, which would keep him involved in the central action as opposed to letting him get spaced out of the play.
They opted for the latter, and if it wasn't already clear that Williams is far more disruptive as a back-line helper than he is as a ball-screen defender, it became abundantly so almost immediately after the substitution was made. In the span of about 80 seconds, the Sixers got an Embiid short-roll jumper, a James Harden and-one layup, and an Embiid dunk out of pick-and-rolls involving Williams as the screen defender. After the last one, Williams was pulled for Derrick White.
Those plays weren't necessarily Williams' fault (though he got juked pretty badly on Harden's layup); they just demonstrated the impact of taking him out of help position. And getting him off the floor was a huge win for the Sixers, who ultimately put together a 23-8 run after subbing in Niang and seemed to have taken control of the game. They hadn't, of course, and in the fourth quarter Williams was back out there blotting out the rim, this time while helping way off of the ice-cold De'Anthony Melton.