Pressure has tripped up Tom Brady several times this season. (Peter Foley/EPA)

For an incredible 10th time since 2001, the Patriots and Tom Brady are back in the AFC Championship Game. The Brady-era Patriots are 6-3 in this round, although fans are well aware that two of the three losses came in Denver, and two of the three losses came against teams led by Peyton Manning. Of course, traveling to Denver to face Manning is precisely what the Patriots face this Sunday, which is how the team’s 2013 season ended. But don’t let history cloud the facts: The Patriots are 3-point favorites, and given the Broncos’ offensive struggles this year, that line may only increase.

As usual, the case to beating the Patriots starts with getting pressure on Brady. There’s good reason for that: in the Brady era, New England has lost as a favorite in the postseason five times, and the opposing team’s pass rush was a factor in each game. On average, Brady was sacked three times and was hit 6.8 times in those games. Getting to Brady is much easier said than done, and it’s hardly a guarantee of victory, but it does seem to be the most recognizable path to success for Denver.

Patriots under pressure

Year Opp Pts Cmp Att Yds TD Int Sacks QB Hits
2012 BAL 13 29 54 320 1 2 0 7
2011 NYG 17 27 41 266 2 1 2 8
2010 NYJ 21 29 45 259 2 1 5 7
2009 BAL 14 23 42 132 2 3 3 3
2007 NYG 14 29 48 229 1 0 5 9
Avg  — 15.8 27.4 46.0 241.2 1.6 1.4 3.0 6.8

According to ESPN Stats & Information, Brady was pressured on 26 percent of dropbacks this season, which ranked 17th out of 35 qualified quarterbacks. This means pressuring Brady is not as difficult as it has been in past years, and that is particularly true as of late: he was pressured on 32.4 percent of his passes during his final eight regular-season games, and 28.9 percent of the time in the team’s game against Denver in Week 12.

That makes the Broncos a scary matchup for New England: Denver’s defense pressured opposing quarterbacks on 34.7 percent of dropbacks, best in the NFL. The Broncos pass rush is led by Von Miller, who had 11 sacks and 32 hurries (sixth most in the NFL). But DeMarcus Ware (16 hurries in 11 games), Malik Jackson (16) and Derek Wolfe (13 in 12 games) can all bring the pressure as well.

While all quarterbacks are worse under pressure, Brady has seen his play decline more than most this season when the defense gets through. This season, Brady had a Total QBR of 64.4, which ranked 11th in the NFL. But while Brady ranked 12th in Total QBR when not facing pressure with a 79.4 Total QBR, that dropped to just 12.7 (19th overall) when under pressure. This is particularly apparent when it comes to completion percentage: Brady completed 71.1 percent of his passes when not under pressure (seventh-best), but just 39.2 percent when under duress (26th).

Completion percentage is often overrated, and it isn’t a critically important stat generally, but the Patriots are a unique offense. As a general rule, completion percentage is highly correlated with winning, but a large reason for that is leading teams tend to throw conservative passes and trailing teams tend to throw aggressive ones. Thus the stat is a result of success even more than a cause of it. (In other words, completion percentage is a lot like rushing attempts, where the best teams tend to fare well in this metric, but in a misleading way.) This season, teams won 58.4 percent of games when completing at least 60 percent of passes, and just 33.3 percent of games when completing fewer than that. But the Patriots were more extreme, winning 11 of 12 when completing at least 60 percent of passes, with the one loss coming in overtime against the Jets. On the other hand, New England lost three of the four games this season when Brady completed fewer than 60 percent of passes, and the one victory came when New England held Buffalo to just 13 points.

The reason completion percentage matters for New England is because the Patriots don’t really have a running game, at least not in any traditional sense. Against Kansas City on Saturday, the Patriots threw on 24 of the team’s first 26 plays. All game, Patriots running backs had just seven carries, with Steven Jackson — signed in December — taking six of those carries and gaining just 16 yards. In the regular season game against Denver, the Patriots began the game by calling 18 passes to just two runs on the team’s first six drives.

New England passes to get ahead, and that only works when Brady is stringing together completions. That’s why Brady’s significant drop in completion percentage under pressure means getting pressure is so significant. And, again, Denver may be Brady’s kyrpotnite: the Broncos defense allowed opposing quarterbacks to complete 67.4 (13th-best) percent of passes when they were not under pressure, but that figure dropped to just 40.9 percent (ninth) when under duress by Broncos defenders. Denver allowed just four touchdowns against seven interceptions when they were able to bring pressure, and got to the quarterback for an NFL-high 52 sacks.

With all the focus on pressuring Brady, you may think that Miller, Ware, or one of New England’s offensive lineman would be the key to the game. But the difference-maker may wind up being Julian Edelman, who is Brady’s security blanket against the pressure. Without a pass-catching running back like a Shane Vereen (now with the Giants) or Dion Lewis (36 receptions in six games before tearing his ACL), Brady looks to Edelman as his hot receiver to understand how to get open quickly against the blitz.

Against Kansas City, Edelman caught 10 of 16 targets for 100 yards. Edelman missed the Broncos game with a broken foot, which may have been enough to tilt the game. During the regular season, Brady completed 59.4 percent of his passes — and went 3-4 — in the seven games Edelman missed. Meanwhile, the Patriots went undefeated, and Brady completed 68.0 percent of his passes, in the 10 games (including playoffs) where Edelman was healthy.

Many games turn on the effectiveness of the pass rush and completion percentage, and both metrics can be artificially inflated or depressed based on the way a game unfolds. But few teams are as dependent on stringing together completions as New England, and no team has been better at bringing pressure than the Broncos. That makes this AFC Championship Game a fascinating one, between the most pass-heavy offense in football and the defense best known for bringing the pressure.

Chase Stuart writes about the historical and statistical side of football at his site,