On May 8, 1878, Paul Hines was credited with a triple play which was correct for the "rules in play." However, by modern rules it was an unassisted double play with a throw to second base for the third out.

Bill Wambsganss Triple Play during 1920 World Series
(Source: Hall of Fame Collection)
On October 10, 1920, Elmer Smith hit the the first grand slam in World Series history. What is the relevance? During that same game Wamby also turned the first & only unassisted triple play (Read the entire Cleveland Times article on our 1920 World Series page) in post season history.
Did you know that George Burns and Johnny Neun are the only first-baseman in Major League history to ever turn an unassisted triple play? Breaking down all fifteen by position shows us two by first baseman, five by second basemen and eight by shortstops.