The end came suddenly for a Steelers defensive nucleus that finished in the top five for an astonishing six consecutive years from 2007 through 2012.
As perennial standouts such as Troy Polamalu, Casey Hampton, Aaron Smith and Ike Taylor reached the end of the line, Hall of Famer Warren Sapp minced no words in denouncing the once-vaunted Pittsburgh defense as "old and slow."
The turnaround has been impressive in scope and acceleration.
Upon losing a 35-30 barnburner to the Cowboys in Week 10, Keith Butler's defense ranked 25th in yards allowed, 28th in yards allowed per play and dead-last in sacks. Since that benchmark, the Steelers are third in yards allowed, second in yards allowed per play and first in sacks during a nine-game winning streak.
"We've evolved schematically," coach Mike Tomlin recently explained, via Dale Lolley of the Observer-Reporter, "but we've probably evolved schematically because of the evolution of the individuals that execute the schematics."
In other words, this is a materially different defense than it was three months ago. The Steelers started shutting offenses down when they promoted the rookie duo of cornerback Artie Burns and strong safety Sean Davis into the starting lineup at midseason. Shortly thereafter, they ditched the early-season rotation at outside linebacker, turning edge-rushing duties over to an ageless James Harrison and 2015 first-round pick Bud Dupree.
The final key has been the emergence of defensive end Stephon Tuitt and inside linebacker Ryan Shazier as consistent stars, playing at a Pro Bowl level. Perhaps the fastest linebacker we've seen since former Bears All-Pro Brian Urlacher entered the league as a freakishly talented former New Mexico safety, wide receiver and kick returner, Shazier has recorded an interception in four consecutive games -- tied for the longest streak by a linebacker since the 1970 AFL-NFL merger.
"The more this season went on," Tuitt explained in December, "the more we grew together, the more we learned from each other, the more we learned how people play, and the more we are just continuing to have dominant performances."
When the Pittsburgh defense takes the field in New England, it will start seven players from the last three draft classes since Sapp deemed them "still too old and slow" in the summer of 2013: