'Django Unchained' Mandingo Fighting: Real Or Not?

If you haven't seen "Django Unchained" and are super averse to knowing anything about the film's plot, now would be a good time to click elsewhere.
A key plot point of Quentin Tarantino's western-blaxploitation-revenge movie is the supposed sport of Mandingo fighting, in which two (black) slaves fight in a bare-knuckle death match, for no reason other than the (white) slaveowners' enjoyment. The search for the perfect Mandingo, or wrestler, is the vehicle Tarantino (who, of course, wrote and directed the film) builds the rest of his movie around. But a bevy of historians say it probably never happened.
One expert tells Slate (which says that "no slavery historian we spoke with had ever come across anything that closely resembled this human version of cockfighting") that the very notion that Southerners would send off their slaves to die is logically flawed. Given the entire structure of slavery was based on economic expedience, it just doesn't make much sense that a slaveowner would be willing to lose one of his strongest and healthiest men to death for sport.
NextMovie cites Edna Greene Medford, a professor and the chair of Howard University's history department. Turns out she hasn't seen any evidence of Mandingo fighting either:

"My area of expertise is slavery, Civil War, and reconstruction and I have never encountered something like that. It was rumored to have occurred. I don't know that it was called Mandingo Fighting, however, but there were all sorts of things going on in the South pitting people against one another. To the death, I've never encountered anything like that, no. That doesn't mean that it didn't happen in some backwater area, but I've never seen any evidence of it."

Slate notes that a number of films have used Mandingo fighting as a plot device, including the 1975 film "Mandingo" -- one of Tarantino's "favorite" movies.
Of course, Tarantino is free to embellish history as he sees fit. Adding color to a piece of historical fiction is more complicated, however, when one suggests the film was not even as violent as slavery. Tarantino bristled at criticism that "Django" is too violent by reminding audiences that slavery was much worse than anything depicted in the film. Via the Guardian:

"We all intellectually 'know' the brutality and inhumanity of slavery, but after you do the research it's no longer intellectual any more, no longer just historical record – you feel it in your bones. It makes you angry, and want to do something … I'm here to tell you, that however bad things get in the movie, a lot worse shit actually happened ... When slave narratives are done on film, they tend to be historical with a capital H, with an arms-length quality to them. I wanted to break that history-under-glass aspect, I wanted to throw a rock through that glass and shatter it for all times, and take you into it."

It may well be true that "a lot worse shit actually happened." Just (probably) not Mandingo fighting.