Pinpointing exactly why the Giants have been able to go from a 23-10 loss to Rex Grossman to the brink of a Super Bowl berth is fairly difficult, but there's no doubt that getting healthy on defense played a role.
Osi Umenyiora's return from an ankle injury and Justin Tuck's return from the island of self loathing have put the team's defensive line back in form, allowing them to rush just four players at opposing quarterbacks so that their often overmatched secondary isn't left exposed the way it was earlier in the season.
Other factors have certainly played a role, but we know the Giants get a big chunk of their success from the front four.
They aren't the only team that likes to utilize a minimal number of pass rushers to get the job done. The 49ers also prefer to keep things simple when they get after quarterbacks, something that has worked out pretty well for them this year.
San Francisco works out of a 3-4 base, so you won't see any all-defensive end packages from them on Sunday but you will see a lot of four-man rushes coming at Eli Manning.
Justin Smith, Aldon Smith, Ray McDonald and Ahmad Brooks all piled up good sack numbers this season and, like the Giants, their ability to get after quarterbacks all by themselves allows the secondary to cover receivers all over the field.
When the 49ers dropped seven or more into coverage this season, they made it incredibly difficult on opposing passing attacks and even the Saints spent most of last week struggling to gain traction through the air thanks to the blanket of defensive backs they faced on every play.
That history should be worrisome to the Giants.
It should be worrisome because the 49ers almost totally shut down opposing running games this season, going 14 games before allowing a rushing touchdown, and because the 49ers' ability to rush just four plays into a Giants weakness.
Lost in the four straight victories has been the fact that the Giants' offensive line hasn't played particularly well in any of the games.
Manning covers up for a multitude of sins, but the fact is that the Giants haven't faced a team with the 49ers' ability to rush the passer during their streak.
Manning does a terrific job when faced with a blitz because he can recognize its origin and attack the spot left vulnerable.
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Against a four-man rush, though, Manning doesn't have that area to exploit and, if his offensive line breaks down, he won't have anywhere to go with the ball if he's pressured.
His numbers in such situations this season are fairly ordinary and he was picked off twice against the Niners the first time the teams met this season.
So the offensive line needs to step up its game because the Giants' best chance of beating the Niners rests with the ability of Manning to hit plays down the field to Hakeem Nicks and Victor Cruz. If they pick up the rush, the Giants should be able to do that often enough to win.
If they can't, Manning will get hit and he will be less effective than the team needs him to be to win. It's a tough task for the offensive line, but the rest of the Giants have stepped up their games in recent weeks so it is just their turn to join the party.
Josh Alper is a writer living in New York City. You can follow him on Twitter and he is also a contributor to Pro Football Talk.
