Simplify the following text for a Grade 9 native English-speaking person.
Original: In a political upset , Childers was elected the fourth President of Ireland on 30 May 1973 , defeating Tom O'Higgins by 635,867 votes to 578,771 .
Simplified: Childers was elected the fourth President of Ireland on 30 May , 1973 , defeating Tom O'Higgins by 635,867 votes to 578,771 .