Is there a moment in sports history we can cite in which professional
wrestling moved from a legitimate sport to a pre-arranged burlesque?
I'm interested in knowing whether we can attribute the shift to a
particular promoter, a specific venue, a certain date. Or did it
happen very gradually, in different parts of the country, at different
times? If so, how did the last legitimate wrestlers distinguish
themselves from those who were engaging in the choreographed variety?

Hi! Thanks for the question.

There are some independent sources out there in the internet
discussing the history of pro wrestling and pro wrestlers. I will
first cite here the MSN Encarta Encyclopedia Online since it is quite
reputable and well known. According to Encarta, professional wrestling
was fake from its earliest history.

"In the early days of professional wrestling, wrestlers toured the
country and took on opponents from the audience. Many of the audience
participants were approached beforehand and knew that they were
supposed to lose to the star. Tom Jenkins and Frank Gotch were
well-known performers of this early era, which ended about World War I
(1914-1918)."

"In the 1930s carnivals began to include wrestling matches. Future
wrestling promoters saw the sport?s popularity and began to book
matches in arenas. Early in the sport?s history wrestlers would hold a
move such as a headlock for up to five minutes, but in the 1930s
promoters began presenting matches in which the holds were
abbreviated, allowing for more action. For example, instead of holding
a headlock for five minutes, a wrestler might hold it for one minute
and then release the opponent in order to execute another move."

"Professional Wrestling"
http://encarta.msn.com/encyclopedia_461510921/Professional_Wrestling.html


Let us look at some of the websites out there providing bits of this
history. By reading this write-ups about Tom Jenkins and Frank Gotch
it seems that pro wrestling was real.

"Tom Jenkins Tough As Barbed Wire"
http://www.1wrestlinglegends.com/columns/hewitt/mh1.htm

"Frank Gotch"
http://www.wrestlingmuseum.com/pages/bios/gotch2.html


Search terms used:
history pro professional wrestling
"Tom Jenkins" "Frank Gotch"

I hope these links would help you in your research. Before rating this
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Easterangel-ga                 
Google Answers Researcher

My late father was a wrestling fan. He used to grumble quite a lot
about how the sport began to degenerate into a sideshow act in the
1950s. In my dad's view, "real" wrestling turned into "showbiz"
wrestling largely because of a wrestler known as "Gorgeous George,"
whose heyday came right as television first discovered wrestling.

"Before there was Buddy Rogers, before there was Ric Flair, before
there was Hulk Hogan, before there was the Rock, there was the man who
pioneered flamboyant ring style, Gorgeous George. George innovated so
many of the things we take for granted in wrestling today like
bleached blond hair, ring entrances with music, colorful robes, and
preening before his match. At the time, no one had ever seen anything
like 'The Human Orchid', and George became one of the first television
stars ever."

http://www.awcable.com/wrestlingclassic_superstars.htm#GG

I wouldnt say wrestling ever evolved in the area of changing real to fake.
Real wrestling still exists today in colleges and in the olympics.
Fake wrestling such as the WWE,is completely pre-arranged.
It started off as a rather low-budget pre-arranged sport and did
however evolve into the huge specatcle it is today.  And alot of that
is attributed to names like Hulk Hogan, the Rock and Steve Austin. 
And of course the man behind and in front of the curtain Vince
Mcmahon.

A turning point would be Lou Thesz unifying the titles:

"Lou Thesz unifies the NWA World Heavyweight title with the National
Wrestling Assocation's World title on July 20, 1948. He recieved the
NWA World Heavyweight title on November 27, 1949 when Orville Brown
was injured in a car accident and couldn't defend the title. Lou Thesz
then went to unify the titles of the American Wrestling Assocation
World title on July 27, 1950 and with the World title recognized by
Los Angeles Olympic Auditorium wrestling on May 21, 1952. [Credit for
this information goes to Great Hisa's Pro-Wrestling Title Histories.]"
http://www.titlehistories.com/NWA%20World%20Heavyweight%20Title.htm