Ryan DempsterĀ of theĀ CubsĀ andĀ Homer BaileyĀ of theĀ RedsĀ both celebrate their birthday by pitching against each other. It is believed to be the first time in major league history that opposing starting pitchers are both pitching on their birthdays.

On May 3, 2012 — Ryan DempsterĀ of theĀ CubsĀ andĀ Homer BaileyĀ of theĀ RedsĀ both celebrate their birthday by pitching against each other. It is believed to be the first time in major league history that opposing starting pitchers are both pitching on their birthdays.

Source:
Baseball Reference May 3