PITTSBURGH — In an endlessly surprising year for the N.F.L., filled with attacks on the league from a sitting president, a politically charged debate over the national anthem, and more controversy over the league’s handling of its concussion protocol, perhaps what happened here Sunday on a frigid afternoon was only fitting.

The Jacksonville Jaguars, a franchise that had not won a division title since Bill Clinton was president, upset the Pittsburgh Steelers, those mighty six-time Super Bowl champions, by 45-42 in a divisional-round game that was not actually that close. The result upended expectations for the rest of the playoffs.

The Steelers were supposed to be the last team capable of stopping the New England Patriots, who will appear in their seventh consecutive conference title game next week. Instead, the Jaguars — that’s right, the usually hapless Jaguars! — will try to deny the Patriots a third Super Bowl berth in four years. The N.F.L. will have to wait at least another year for a Patriots-Steelers showdown that would have been a shot in the arm to the league’s sagging television ratings.

Maybe hubris played a part. The Steelers finished the season with 13 wins and might have claimed home field through the A.F.C. playoffs had a touchdown pass to tight end Jesse James in a game against the Patriots last month not been overturned by a controversial call. The Steelers have burned for a second shot at New England ever since.