Packers LB Clay Matthews (left) and Broncos LB DeMarcus Ware will be all over the quarterbacks in this matchup. Jeff Hanisch/Chris Humphreys - U USA TODAY Sports

Aaron Rodgers and Peyton Manning.

Two of the NFL's greatest quarterbacks will go head-to-head on Sunday night, when the Green Bay Packers visit the Denver Broncos in a battle of unbeatens.

The main storylines will have to do with these two passers. Rodgers is coming off an MVP season, and his dynamic ability makes his Packers a favorite to win this year's Super Bowl. Manning is looking for one last championship before calling it a Hall of Fame career.

But the real story has little to do with either of these franchise quarterbacks. The Packers and Broncos are both undefeated because they have dominant defenses. Green Bay's unit ranks first in the NFL with an average of 16.8 points allowed per game; Denver's platoon is tied for second with an average of 17.0.

The Packers are a well-balanced unit, with impact playmakers at all levels of the defense. Manning will have to be aware of linebacker Clay Matthew's whereabouts on every play, and he must be wary of Green Bay's dangerous rookie cornerbacks -- Damarious Randall and Quinten Rollins.

Rodgers has only two interceptions this season, but he hasn't seen a ball-hawking unit quite like Denver's defense yet this year. The Broncos are second in the NFL with 17 takeaways, four of which have been returned for touchdowns. Veteran outside linebacker DeMarcus Ware leads the league's most productive pass rush (26.0 sacks) with 4.5 sacks.

Rodgers and Manning may headline this Week 8, but the Green Bay and Denver defensive units are almost certain to steal the show.

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