Perhaps, depending on your definition of knuckleball.

Clarence Mitchell appeared twice (in 1920 for Brooklyn and in 1928 for St. Louis), in a long relief role in each case. Mitchell probably threw more of a knuckle-curve than what today is deemed a knuckleball, but it was called a knuckleball at the time.

Bearden, on the other hand, threw both a knuckleball (using the middle three fingertips of his pitching hand on top of the ball) and a spike curve (using the bent middle finger of his pitching hand on the ball). The Sporting News had illustrations of his grips in the issue that covered the World Series in 1948.

More recent left-handed knuckleball pitchers had some success in the major leagues–notably Mickey Haefner in the 1940s and Wilbur Wood in the 1960s and 1970s–but never made it to the playoffs.