Forlan was given the prize after his five goals helped Uruguay to an unexpected fourth place at SA2010.
But Spain manager Del Bosque was more impressed with Argentina star Messi.
"Apart from our own [players] I preferred Messi," he said. "Each game he played he made 20 chances to score, he is a phenomenon.
"We would have liked it to have been one of us. But Messi deserves the Golden Ball more than Forlan."