Garcia, who made the cut on the number at 5-over par, signed for a 4 on the par-4 17th hole, when he in fact recorded a 5. He shot a 4-over 74 in the third round, though that score was not official because of the disqualification.
In tournament golf, players exchange scorecards and keep each other's score. Garcia was playing alongside Boo Weekley, who wrote down the score down incorrectly. At the end of the round, it is the player's responsibility to check the card for accuracy and Garcia didn't do that.
Garcia had left the course and was not available for comment when his disqualification was announced.
'It's my fault for putting the wrong score in, but it's his fault for not checking,' said Weekley, who shot 5-under 65. 'I just said 'Sergio, I put a 4 but in fact you had a 5.' He said, 'That just puts the icing on the cake.''
Indeed, it has been a rough week and a rough summer for Garcia. On Thursday, Garcia got into an animated argument with a course official who put his group on the clock as they made the turn. After an opening-round 70, he shot 75 the second day to fall out of contention.
At the British Open, Garcia lost in a playoff after barely missing a putt on the 18th hole that would have won the tournament. In a memorable post-round news conference, he complained about all the breaks that go against him and all the bad luck he has.
'You know what's the saddest thing about it?' Garcia said. 'It's not the first time. It's not the first time, unfortunately. So, I don't know, I'm playing against a lot of guys out there, more than the field.'
Weekley said he called Garcia back to the scoring tent after the scorecard had been signed, in hopes the mistake could be fixed. But officials said once Garcia had left the 'scoring area perimeter,' there was no correcting the problem.
'He just took off,' Weekley said. 'I called him back down and tried to get him before he got all the way up the stairs.'
The most famous scoring gaffe came at the 1968 Masters when Roberto De Vicenzo signed for the wrong score. De Vicenzo actually signed for a higher score on a hole, so he wasn't disqualified, but he had to take the extra stroke, knocking him out of playoff with Bob Goalby.
In 2003, English journeyman Mark Roe was disqualified after shooting 67 in the British Open. Both he and Jesper Parnevik were disqualified because they forgot to exchange scorecards before they teed off. Roe was only two strokes off the lead.
Garcia's blunder was nowhere near as dramatic. With a three-day score of 9 over, he would have been tied for 63rd in the 72-man field, with about half the players still out.