Technically NOT Chaplin's first appearance as the Tramp.
This is the first short released to feature the Tramp, but the one where the character was actually born (in a spur-of-the-moment before filming) was "Mabel's Strange Predicament" (filmed right before "Races"). Though this one is funny, it's interesting to watch him testing the waters in his first outing as the Tramp in "Mabel's Strange Predicament".