Phil Mickelson took full responsibility for his error at the Presidents Cup as the United States saw their lead over the International team cut to one point.
Mickelson – playing in his 11th Presidents Cup– was hit with a penalty at the seventh hole in Incheon on Friday after he violated the 'one-ball condition' during his fourballs match with Zach Johnson against Jason Day and Adam Scott.
The ruling means that players cannot switch golf ball models during the round and is known as a one-hole adjustment.
As a result of his mistake the American was handed a penalty and as Johnson lost the hole it allowed their opponents to move ahead.
"It's not their [the officials'] responsibility for me to know the rules and if I had a question I should have asked," he told The Golf Channel. "We never had a non-one-ball rule that I can think of in these formats, and I don't know why I asked after I hit it. I just double checked.
"[But] it helped me get a little bit more focused because I was so angry at myself, that ended up with me making a birdie and eagle at 11 and 12 and got a little bit re-focused."
Despite the mistake Mickelson and Johnson battled back to earn a half, but the 45-year-old rejected claims it felt like a win after rescuing their difficult situation.
He added: "It doesn't feel like a victory, I made a mistake, I've never even heard of a match adjustment, that one's new."
The United States lead the International team 5.5 to 4.5 after the first two days of play at the Jack Nicklaus Golf Club Korea.