Players are permitted to carry no more than 14 clubs and Austin discovered that he had 15 with him as he played the par-three third at Oak Hill Country Club.
The 49-year-old, a four-times winner on the US Tour, immediately declared the extra club out of play and reported the mistake to a rules official once he completed the third hole.
Under the rules of golf, "the player must not start a stipulated round with more than 14 clubs." The penalty for a breach of this rule is two strokes for each hole where the extra club is carried in the bag.
Former world number one Ian Woosnam was the most notable victim of this rule at a Major, being assessed a two-stroke penalty in the final round of the 2001 Open at Royal Lytham where he was in contention.
Welshman Woosnam was informed of the breach by his caddie after he had nearly holed out in one at the start of the round, and he ended up finishing in a tie for third at the championship.