Defense Once Won N.F.L. Titles, but No Longer Ray Lewis, right, and the Baltimore Ravens beat the Giants in the 2001 Super Bowl after allowing just 10.3 points a game. As the Pittsburgh Steelers, their top-ranked defense shredded by one of the N.F.L."s worst passers, trudged into the off-season and a cold Denver night last Sunday, it was tempting to wonder if they might someday be viewed as a relic from a fading era. Pittsburgh has won six Super Bowls, more than any other franchise, on the power of a defense so immovable it is called the Steel Curtain. But the curtain was dented by Tim Tebow and his sub-50-percent completion rate, exposing a flaw that ultimately doomed the Steelers: their offense could not score with the ease and rapidity of a pinball machine, as much a staple of the current N.F.L. game as Jack Lambert's jarring hits were for a previous generation. In a season when scoring was at a 46-year high, the Steelers" early exit from the playoffs spotlighted a sea change in the way games are being played - and won. That tide overwhelmed the N.F.L. this season and threatens to reconfigure the traditional underpinnings of championship-caliber football. The legendary Alabama coach Bear Bryant is credited with the adage that "offense sells tickets, but defense wins championships." Perhaps that was true three decades ago, when Bryant was coaching. But maybe not this year. "Defense may get you there, but then your quarterback has to win it," said Bruce Arians, the Steelers" offensive coordinator. The old adage is that you play defense and run the ball. That doesn't happen anymore in the N.F.L. It's great quarterback play. It's happened the last five years - a great quarterback won the Super Bowl. The top seeds in the A.F.C. and the N.F.C. - the New England Patriots, who play the Broncos on Saturday night in the divisional round, and the Green Bay Packers, who host the Giants on Sunday - had, statistically, the worst defenses in the N.F.L., giving up more yards than any other teams in the regular season. Their offenses, though, both rank in the top three in the league in points scored, where they are joined by the New Orleans Saints, who play the San Francisco 49ers on Saturday. In their most recent games, the Patriots spotted the Buffalo Bills 21 points in the first quarter and roared back to win, 49-21, while the Packers - playing with their backup quarterback, Matt Flynn - beat the Lions, 45-41, in a game in which Flynn and the Lions" Matthew Stafford combined for 1,000 yards passing. If defense is dying, its death knell could come in San Francisco on Saturday. The 49ers constructed their rapid resurrection this season on the back of their defense - even though Coach Jim Harbaugh is a former quarterback - giving up the second-fewest points in the league, an average of 14.3 per game, behind only the Steelers. They did not give up a rushing touchdown in the first 14 games of the season. It is an old-school approach that relies on the offense to play soundly but not spectacularly. They were ranked 26th in yards but a respectable 11th in points scored (23.8 per game). The Saints, though, play offense as if on roller skates, scoring the second-most points, an average of 34.2 per game, behind the Green Bay Packers and gobbling up yardage in big chunks: 80 of Drew Brees's completions were for at least 20 yards. In five of their last seven games, including last week's 45-28 wild-card victory over the Detroit Lions, the Saints scored at least 42 points. "This year's been a crazy year," said Baltimore Ravens safety Bernard Pollard, who called the Saints-Lions game a shootout. It's one of those years where you don't understand why things keep happening. You're putting up 35, 40 points a game. The team's putting up 25, 30 points on your defense and you're winning. I think that's going to catch up to you. Pollard hopes so. The Ravens have a routinely stout defense and are ranked third in points allowed this season. But recent playoff runs have been undone by their offense, and they are 12th in points scored. This season, two quarterbacks, Brees and Tom Brady, broke Dan Marino's single-season passing mark of 5,084 yards. Detroit's Matthew Stafford also topped 5,000 yards, and all three made the playoffs. Before this season, only two quarterbacks - Marino and Brees - had gone over 5,000 yards. Three quarterbacks threw at least 40 touchdown passes; no other season has had more than one. The 1988 49ers, the last of the Bill Walsh-Joe Montana championship teams, ranked seventh in the league with 23.1 points per game in the West Coast offense. In 2011, the 49ers averaged 23.8 points per game but ranked only 11th in scoring. The top-scoring team in 1988, the Cincinnati Bengals, averaged 28 points per game. The top-scoring team in 2011, the Packers, scored a full touchdown more, averaging 35 points per game. "If I'm sitting there, do I want to bet on San Francisco being able to play three defensive games to shut down three great offenses?" said Tony Dungy, the analyst for NBC's "Football Night in America." Or do I bet on Drew Brees, and Aaron Rodgers and Tom Brady? I bet on the quarterbacks. Ben Shpigel, Rob Reischel and Peter May contributed reporting.