The mistakes came to light when a fan, who was following Yang's group Saturday, saw the mistakes on a Web site after returning home from the tournament.
Yang, the South Korean player who beat Tiger Woods to win last year, signed for a 4 at No. 12, when in fact he made a 5. On 17, he signed for a 3 when he actually made a 2.
This meant his finishing score of 2-under 70 was correct. However, he was disqualified for the mistake at 12 -- signing for a figure lower than the actual score. Signing for a higher score isn't punishable.
After three rounds, Yang was 7 under and in a group of seven players who were seven shots off the lead.
In a statement, Yang accepted responsibility.
'I'm shocked,' he said. 'It's unbelievable. At the end of the day, though, it's my fault for not checking the scores.'