This could be the last knockdown, drag-out defensive struggle.

Tennessee’s matchup with Pittsburgh today at Nashville, Tenn., is the only divisional playoff game between two top-10 defenses. A Tampa Bay-Philadelphia NFC title game and maybe a Super Bowl are the only other possibilities this postseason.

It may already be too late. The Steelers were torched last week by Cleveland’s passing attack, surviving when Tommy Maddox threw fourth-quarter touchdown passes himself.

Defense is supposed to win championships, but nothing about this season has gone by the book. From the time New England spread the field and lit up the Steelers’ on the opening Monday night, defense has been on its heels.

If defense ultimately wins out, it will have to stem an unprecedented tide of touchdowns and passing.

The Steelers and Titans were built on running and defense, but running backs Jerome Bettis of Pittsburgh and Eddie George of Tennessee are dinosaurs. The ailing Bettis has given way to quicker, smaller Amos Zereoue. George averaged 2.8 yards a rush against the Steelers on Nov. 17.

In today’s NFC game against Atlanta, Philadelphia quarterback Donovan McNabb will be making his first start since breaking his right ankle on Nov. 17.