At the Seventh Street Park in Indianapolis, future 300 game winner Mickey Welch becomes the first pinch hitter in major league history. Although the Giants right-handed pitcher strikes out in his historic plate appearance, New York prevails, beating the Hoosiers, 9-6.

On August 10, 1889 — At the Seventh Street Park in Indianapolis, future 300 game winner Mickey Welch becomes the first pinch hitter in major league history. Although the Giants right-handed pitcher strikes out in his historic plate appearance, New York prevails, beating the Hoosiers, 9-6.

Source:
Baseball Reference August 10
National Pastime
Retro Sheet
Hall of Fame
SABR Games Project
Replay The Game