It will be the rarest of rarities Sunday afternoon as the Denver Broncos will be a home playoff underdog for only the second time in the 22 post-season games they’ve hosted in the Mile High City.

It also will be only the ninth time a road team is favored in the NFL’s conference championship game round during the last 30 years as Tom Brady and the defending Super Bowl-champion Patriots have opened this week as slight favorites in Sunday’s title tilt, and the line has crept up to 3.5 points at some sportsbooks.

Going back to that first note, let’s first establish that we have asterisks on first two Denver home playoff contests in 1977 as the ProFootballReference.com point-spread database goes back through the ’78 season.

Still, even excluding those wins in ’77 over the Steelers and Raiders, of the next 19 playoff games hosted by the Orange & Blue, the 12-4 defending AFC-champion Steelers of 2011 were the only team to kick off a post-season contest in Denver as a visiting favorite. The Steelers were 7.5-point pick to beat Tim Tebow and the 8-8 AFC West champs in that wild-card contest, but he Broncos, as you well know, prevailed 29-23 in overtime.

Including that memorable win, the Broncos are 14-11 straight-up as home underdogs over the last 20 seasons. The latest wins, of course, on that list were the Orange & Blue’s 29-10 and 30-24 victories over the Packers and Patriots, respectively, this season in games in which they entered as 2.5-point underdogs.

Moving ahead to this past Sunday’s 23-16 divisional-round victory over the Steelers, it gives the Broncos an all-time home playoff record of 16-5.

The Patriots, meanwhile, are 6-9 in the franchise’s 15 road post-season outings, including a 3-3 mark during the Bill Belichick/Brady Era (2000-present). For all their success, the Pats have been favored in one of those 15 games, entering the 2004 AFC Championship Game in Pittsburgh as a field-goal favorite and emerging with a 41-27 win en route to their third Super Bowl win in four seasons.

That game is also included on the short list of conference-championship tilts (eight of 60 total games) from 1985-14 where the road team was favored. As you’ll see in the following list, the visiting favorites won six of those games straight up with only the 2000 Vikings and 2008 Eagles failing to advance to the Super Bowl.

Per ProFootballReference.com, here’s the full list of road conference championship-game favorites in chronological order:

• 1988 NFC: 49ers (-2) beat the host Bears 28-3
• 1992 AFC: Bills (-2.5) beat the host Dolphins 29-10
• 1997 NFC: Packers (-1.5) beat the host 49ers 23-10
• 2000 NFC: Vikings (-1) lost to the host Giants 41-0
• 2004 AFC: Patriots (-3) beat the host Steelers 41-27
• 2008 NFC: Eagles (-3.5) lost to the host Cardinals 32-25
• 2010 NFC: Packers (-3.5) beat the host Bears 21-10
• 2012 NFC: 49ers (-4.5) beat the host Falcons 28-24

So, in short, we have one trend favoring the Broncos Sunday and the other leaning the Patriots’ way.

Looks like we’re right back to a tight, toss-up game.