The Celtics’ defensive efforts in the series have revolved around one key matchup problem. The Hawks’ frontcourt doesn’t really feature a center. Instead, they have two excellent big forwards in Josh Smith and Al Horford. Both players step away from the basket and can make shots, Smith runs the court like a deer and Horford is very strong inside.

The Celtics have chosen to play Kevin Garnett on Smith and Kendrick Perkins and other centers on Horford. Perkins is clearly having trouble dealing with Horford’s versatility.

“Both guys are tough for Perk because of their speed,” said Rivers. “Surprisingly, it doesn’t make a lot of sense, but the guy who’s guarded Horford the best is P.J. Brown. He’s probably the slowest of the group but he just has unbelievable basketball knowledge, and that allows him to do a good job.”

Perkins, who played well last night in the lane, says he and Garnett help each other out defensively.

“We watch each other’s back. He’s helped me with so much,” said Perkins. “It’s a different coverage with this team. Those two guys are really like two forwards and they’re both athletic, and that makes it difficult because they both like to step out and shoot the jumper.”

-KEVIN McNAMARA