The 35-year-old looped a ball over Palace goalkeeper Julian Speroni from an acute angle to give his side a 2-2 draw at Selhurst Park.
"It was instinctive and to be honest I don't know why I shot from there," he said. "I had a little glimpse of the goalkeeper just out of position and I wanted to direct it back across goal.
"Sometimes you try things and they come off. I was surprised myself. It's up there as one of my best goals."
Defoe's goal was one of eight nominated for the award.