Wahab was charged with using obscene language, while Watson was accused of conduct contrary to the spirit of the game when the two faced each other down in a compelling passage of play during Australia's six-wicket win at the Adelaide Oval.
"The incident happened in the 33rd over of Australia's innings when Watson ignored the umpires' instructions and verbally engaged with Wahab, who, at the end of the over, followed through towards the batsman and used aggressive and abusive language," said an International Cricket Council statement.
Match referee Ranjan Madugalle said: "It was an enthralling contest between Shane and Wahab, but in the closing stages of the match both players crossed that fine line between intense competition and unacceptable behaviour, and this resulted in the sanctions."
Australia will face defending champions India in a semi-final in Sydney on Thursday.