Duke and North Carolina have played a combined 334 NCAA men's basketball tournament games. Together, the programs have been to 36 Final Fours, and this week, when they travel to New Orleans for a showdown on their sport's biggest stage, they'll up the total to 38.
And yet, over eight decades, they have never met in the tournament — until now.
The lack of March Madness precedent in the annals of college basketball's greatest rivalry surprised many fans as the matchup materialized. It seemed illogical, even impossible, that two top-five programs who've met hundreds of times in the regular season and ACC tournament had never crossed paths in late-March or April
But it is less a remarkable improbability, more a function of the tournament's format.
The biggest reason Duke-UNC has never happened in the tournament
There are two main rules, or "bracketing principles," that have kept Duke and North Carolina apart. The most influential: "Each of the first four teams selected from a conference shall be placed in different regions if they are seeded on the first four lines."
In other words, if Duke and North Carolina are among the ACC's top four teams, and if they are legitimate contenders to make deep runs in March — which they often have been — they cannot meet until the Final Four at the earliest.
Furthermore, if they cannot share a region, there's only a one-in-three chance that they'd share a side of the bracket.
So, although the often coinciding strength of the two programs would seem to make them likely March foes, it actually means that, in their best years, more often than not, they've had to romp through the entire tournament and stand together as the last two teams remaining to create this dream matchup.
Since the tournament expanded to its current format in 1985, Duke and UNC have both received top-four seeds 23 times. But of those 23 brackets, only seven have placed the two rivals on the same side. That fraction aligns almost perfectly with what random chance would predict — as does the fact that the one Final Four they both made, in 1991, happened to pit them on opposite sides of the bracket.
Rarely on a collision course
There have, therefore, been 14 modern-era seasons when one or both of the Tobacco Road schools has fallen off the top-four seed lines. In five of the 14, one of the two (Duke twice, North Carolina three times) has failed to make the tournament.
In the remaining nine, other bracketing principles come into play:
"Teams from the same conference shall not meet prior to the [Elite Eight] if they played each other three or more times during the regular season and conference tournament."
"Teams from the same conference shall not meet prior to the [Sweet 16] if they played each other twice during the regular season and conference tournament."
Duke and North Carolina play in the regular season twice every year, and occasionally a third time in the ACC tournament. An ACC tournament meeting has actually never affected bracketing, but these limits further restrict potential matchups.
In those nine remaining seasons, the two rivals have been placed on the same side of the bracket four times (including this year), but only once have they shared a region — in 2004, when UNC was a No. 6 seed and lost in the second round as expected, two wins away from a meeting with the top-seeded Blue Devils.
All of this explains why none of the most common matchups in the tournament's modern era are between conference opponents. The 13 most frequent, according to the NCAA, are:
UNC vs. Villanova (6)
UNC vs. Arkansas (6)
Kentucky vs. Utah (6)
Duke vs. Kansas (6)
Duke vs. Michigan State (6)
UNC vs. Kansas (5)
UNC vs. Michigan (4)
UCLA vs. Iowa State (4)
Duke vs. UConn (4)
Kansas vs. Purdue (4)
UNC vs. Michigan State (4)
Wisconsin vs. Arizona (4)
Florida vs. UCLA (4)
The ACC rival show up plenty on that list — in part because tournament rules put them on collision courses with other blue bloods, not with each other.
The early years
Bracketing principles were less strict prior to the tournament's 64-team expansion. In 1979, for example, UNC and Duke were No. 1 and 2 seeds, respectively, in the same region — but each suffered early upsets, UNC to Penn and Duke to St. John's.
Prior to 1975, though, there were no at-large bids. For its first 36 years of existence, the NCAA tournament featured one team per conference. Duke and North Carolina were both founding members of the ACC in 1953, and before that competed together in the Southern Conference. So, in those old days, by rule, they could not meet in the tournament.
Now they can, only they haven't, not in the 46 times they could have. The 47th time turned out to be the charm.