Super Bowl XLV Preview: Up in the air

Super Bowl XLV is being billed as a battle between two classic franchises. But it'stheir ability to evolve that has the two clubs playing for the NFL championship once again.

The Green Bay Packers and the Pittsburgh Steelers established themselves as NFL titans decades ago Green Bay won the first two Super Bowls in the late-1960s; Pittsburgh won the first four of its record six championships in the mid-to-late '70s with hard-nosed styles built on running the ball and playing tough defence. That thosecharacteristics matched the twocities' blue-collar reputations only made them more appealing.

As these clubs prepare to meet in the Super Bowl for the first time, the Packers still conjure images of Vince Lombardi, the legendary taskmaster whobludgeoned opponents with the primitive Power Sweepon the "frozen tundra" of Lambeau Field. Their black-and-goldfoesrecall Jack Lambert's "Steel Curtain" defence, and the bruising running of Franco Harris or, more recently, Jerome Bettis.

But times change, and so does football.

The ground-based wars of attrition ofold have given way (with the help of rules changes) to a more intricate aerial game, and the ability of the Steelers and Packers toevolve has kept them among the NFL's elite. Green Bay won its third Super Bowl in 1997 with Brett Favre slinging passes downfield, and the Steelers' two most recent title runs, in2006 and '09,were engineered by the daring Ben Roethlisberger.

This year's versions of the Steelers and Packersstill play punishing defence (some things never go out of style), but the running game isnow an afterthought in Green Bay and Pittsburgh, where the success of both teams hinges on a superstar quarterback Roethlisberger for the Steelers and Aaron Rodgers for the Packers.

Those men and the passing defences designed to stop them will likely decide Sunday's game in Dallas, which we break down here:

Super Bowl XLV: Pittsburgh vs. Green Bay (6:29 p.m. ET)

The line: Opened at Packers minus-2.5 and held steady with the exception of some movement with the juice.

The backstory:

Green Bay (13-6) went from the lowest-seeded team in the NFC playoffs to Super Bowl favourites in the span of three weeks by beating what most handicappers considered the best three other teams in its conference in consecutive weeks, all on the road. Rodgers led the way in the first two victories, throwing for three touchdowns each in a 21-16 win over Philadelphia and a 48-21 steamrollering of top-seeded Atlanta. At times overlooked, but just as vital, was the Packers' defence, which kept Michael Vick and the Eagles' lethal running game in check, then forced three turnovers by Falcons golden-boy quarterback Matt Ryan. The D terrorized another passer in the NFC title game, knocking Chicago's Jay Cutler out with a knee injury and intercepting three passes the biggest coming late in the fourth quarter when mammoth tackle B.J. Raji took Caleb Hanie's errant throw to the house. Thatplay all but clinched the Packers' first trip to the Super Bowl since the Favre era.

Pittsburgh (14-4) used its first-round bye as the AFC's No. 2 seed to rest up for a pair of home victories over nasty opponents. After falling behind by two touchdowns to bitter division rival Baltimore, the Steelers' defence rallied the team with a pair of second-half turnovers that each set up a Roethlisberger touchdown pass. The big QB's bomb to Antonio Brown late in the fourth quarter set up Rashard Mendenhall's go-ahead TD run and a 31-24 win. Next, the Jets swaggered into town for the AFC title game, and Pittsburgh promptly put them in a 24-0 hole with scoring runs by Mendenhall and Roethlisberger, and a fumble return for a TD by defensive back William Gay. New York made it interesting in the second half, but Mendenhall's 121 rushing yards and Roethlisberger's key scrambles were enough for a 24-19 win. Now Roethlisberger and the Steelers have a chance to add their third Lombardi Trophy in the last six years.

Inside the stats:

In a sport where contests are increasingly decided in the air,Green Baymakes plays on both sides of the passing game. Rodgers owns the best completion percentage and passer rating of any quarterback in this year's playoffs, and ranks second in yards per attempt and touchdown throws. As a team, Green Bay ranked second in the league at 7.7 yards per pass attempt, offsetting its weakness in the run game (with top back Ryan Grant lost for the year in Week 1, the Packer finished 25th in yards per rush). The defence has more sacks in the playoffs (10, including 3 by relentless linebacker Clay Matthews) and twice as many interceptions (six, including three by sticky-fingered cornerback Tramon Williams) than any other unit, masking a soft run D that finished tied for 22nd in yards allowed per rush.

Some things don't change in Pittsburgh, where rock-harddefenceis still a foundation.NFL defensive player of the year Troy Polamalu helpedhis unit hold regular-season opponents to a league-low 6.3 yards per pass and 3.0 yards per rush the latter ishalf a yard less than any other team despite a bad Achilles that cost the safety two of the last thee regular-season games and has trailed him into the playoffs. But Pittsburgh has evolved on offence since Mike Tomlin took over as coach in 2007, morphing into a pass-first team with the unshakable Roethlisberger at the helm and receiver Mike Wallace emerging as an elite deep threat to complement veteran Hines Ward, who's shown signs of decline.The Steelers tied for third in the NFL this year (right behind Green Bay) with 7.4 yards per pass attempt while ranking in the bottom half in yards per rush.

Tellingnumber: 5. That's the difference between the combined amount of points Green Bay outscored its opponents by in the regular season (148) compared with Pittsburgh (143). It's also just one way of showing how this is one of the most evenly matched Super Bowls in memory. Both teams move the ball well (the Packers a bit better), stop their opponents (the Steelers a bit better), rush the passer, take the ball away and protect it when they have it.

The only glaring weakness appears to be the Packers' running game, but the Steelers excel at stopping the run and the Packers prefer to pass anyway, sodoes it evenmatter?On the other side of the ball, Green Bay wasn't very good at stopping the run either, but the Pittsburgh rushing attackis so-so Mendenhall's explosion in the AFC title game notwithstanding.

So why is Green Bay favoured by almost a field goal?Public perception, mostly.Fans tend to have short memories, and the Packers' impressive march through the NFC gauntlet makes them the trendy choice. But this gameis atoss-up from almost every angle, andwith those 2 points in hand the Steelers look like the slightly more attractive betting option.