NFL fans will have a hard time finding a better matchup than the Green Bay Packers' offense against the San Francisco 49ers' defense to kick off the 2012 season. It's undeniable strength versus undeniable strength Sunday afternoon at Lambeau Field.

A quick look at the numbers also shows two units that were among the very best in football a season ago.

Green Bay's offense scored a whopping 560 points—marking the second most in NFL history behind only the 589 points scored by 2007 New England Patriots—while the 49ers allowed under 15 points a game and stopped the run better then 99 percent of teams from the last generation.

San Francisco allowed just three rushing touchdowns in 2011, and only three teams were able to crack 100 total rushing yards in 18 games.

While most here have a pretty good idea how the Packers have remained dominant on the offensive side of the ball, the dominance of the 49ers defense may be a little harder to explain.

Considering how well our breakdowns here at CheeseheadTV have been received lately, I decided to take another extended look at the film—this time to figure out how the 2011 49ers were able to become such a tough unit to crack. Here's what I found.

2011 49ers Defense Breakdown 

It doesn't take more than one viewing of the 49ers defense to understand the physicality this front seven plays with. These guys like to fly to the football and hit whatever moves. But up front, everything starts and ends with Justin Smith and Aldon Smith.

Here we see the 49ers and Pittsburgh Steelers in Week 15 last season. What San Francisco does on this particular play is a staple of their attacking defense. 

Justin Smith moves a shade inside from the five-technique during this nickel look. Aldon Smith then lines up outside the left tackle. The Steelers counter with more than enough blockers (five offensive lineman, running back) to protect Ben Roethlisberger, no matter what 49ers defensive coordinator Vic Fangio throws at him here.

As this play develops, the Steelers appear to have the 49ers' front-four walled off. But look at the top of the formation. Justin Smith has pushed upfield and a touch outside, driving the left guard into the pocket. Aldon Smith, on the other hand, has patiently waited for the guard to be driven back and the tackle to release. The 49ers' patented stunt with the two Smiths has been successfully put in motion.

Now look where Justin Smith is. He's clearly blocked, but it took both the guard and tackle to get it done. The running back, expecting pressure off the outside of the protection, is completely out of position to step up and block Aldon Smith, who has run clean via the perfectly-run stunt. Roethlisberger does have a dump off to the tight end in front of him, but his eyes may be on Smith, who is bearing down on him. Roethlisberger doesn't get the pass off and the Steelers go from 2nd-and-3 to 3rd-and-8 in a flash.

These stunts with the Smiths are something the 49ers did probably once every three passing downs with Aldon Smith in the game. Expect to see a high volume of them Sunday with Aldon Smith playing a more featured role. That reality puts the pressure on Marshall Newhouse and T.J. Lang to communicate during these stunts, because it's a completely blockable maneuver with the right communication involved. The Packers running backs will also have to be aware of what's in front of them. Even the highly mobile Aaron Rodgers won't be able to escape a defensive look if Aldon Smith is running free at the quarterback.

Before we get off Aldon Smith, let's take one last look at what he brings to the table. In this look below, the 49ers bring nothing more than four-man pressure. Smith is circled on top, facing New Orleans Saints Pro Bowl offensive tackle Jermon Bushrod.

The Saints should have this easily blocked, as two linemen take up both middle rushers and Smith potentially getting chipped on the outside. The pocket initially looks to be a clean one. It's hard to tell in screen grabs, but Smith's violent hands and speed on the edge make this a nightmare matchup for Bushrod.

Smith's hand slap frees him of any extension coming from Bushrod. At that point, it's athleticism vs. athleticism, and Smith is going to win that battle against every offensive tackle in the game. He easily gets around the edge and meets Brees in the pocket just as he's delivering a checkdown.

If there's any one matchup that can turn Sunday's game on its head for Green Bay, it's Newhouse vs. Smith. He's such a polished pass-rusher at his age, and the 14.0 sacks he delivered in limited snaps last season is a clear indication of that. Without help on a majority of snaps, it's hard to envision Newhouse keeping Smith down for 60 minutes Sunday.

Enough of Aldon Smith, however. Let's move on to another reason why this defense is so good.

In the screen grab below, Eagles quarterback Michael Vick has escaped contain of the pocket and is racing towards the green ahead of him. Only linebacker Navarro Bowman stands in his way. It's every defender's worst nightmare, right?

Let's be clear right now: These are not your 2010 49ers, who let Donald Driver rumble through numerous arm tackles on his way to a 60-yard touchdown. When this defense gets its hands on a ball-carrier, consider him on the ground.

This Vick example is a perfect one to display just that, although there's a hundred other examples of the 49ers making a fine open-field tackle last season. Consider these guys the anti-2011 Packers, who couldn't tackle anyone.

Here's Bowman calmly making the stop:

Most defenders would cringe at the sight of seeing Vick race to the open field, but Bowman doesn't panic. He levels his shoulders in pursuit, forces Vick into just one option (outside) and then trusts his ability to bring down the runner. It's Tackling in the Open Field 101. What looked like a sure first down for Vick on 3rd-and-3 turns into a punting situation.

And while were at, let's take a second to recognize just how good Bowman is. If he switched his 53 jersey with Patrick Willis' 52, you wouldn't even be able to tell the difference. In fact, Bowman may be more athletic on plays like these. Willis and Bowman together inside is the best in football, and by a wide margin.

Let's now go to the coaches film to break down a factor Packers fans know all about: Getting turnovers. The 49ers actually tied Green Bay with 38 of them last season.

In this screen grab, the New Orleans Saints line up in a five-receiver set, with Jimmy Graham playing inside to the right and Darren Sproles inside to the left.

The 49ers counter this formation like most NFL defenses would, bringing in the dime look with four cornerbacks and just one linebacker. As the play unfolds, three receivers and Graham run four-verticals, with the hope that at least one option can slip down one of the seams for a big gain. Brees is a master of this throw. As insurance, Sproles runs an underneath route in case Brees feels early pressure or nothing is available down field.

Willis, the lone linebacker on the play, runs step-for-step with Graham down the middle of the field. The safety on the right half of the defensive side brackets the far receiver, who is also well covered. The other safety (Dashon Goldson, circled) hovers around the middle of the field, bracketing Graham but also making himself available to cover the other inside seam. At this point, Brees either thinks he has successfully manipulated Dashon Goldson into doubling Graham or he loses track of him. With a solid pocket around him, I bet Brees' eyes got wide as he sees a potential big throw.

It's not to be for Brees, and Goldson has an easy interception no matter where he goes with the football. Brees ends up picking the inside seam receiver instead of Graham, leaving Goldson a short area to read the throw and step in front. As you can see in the screen grab, Goldson is almost waiting on the throw to arrive.

From there, Goldson returns the interception inside the Saints' five-yard line. Three plays later, Alex Smith hits Michael Crabtree on a short slant, and the 49ers' lead suddenly swells from 7-0 to 14-0. The Packers must avoid these kind of mistakes, because they fuel what can be a sometimes stagnant offense. Like Green Bay, San Francisco became adept at turning interceptions and fumbles into points.

It's very clear to me that the 49ers represent the best defense the Packers have faced in some time, including the New York Giants (In fact, the Packers did not play a single team ranked in the top-11 of scoring defense a season ago). San Francisco can get to the quarterback with four rushers, they make every tackle and the game-changing plays are abundant.

The 49ers will make Green Bay work for every point it scores Sunday. Their film from a season ago proves that.