As Americans gear up for Monday opener with Ghana, they take note of referees' key decisions

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The U.S. players are preparing for any circumstance when it comes to calls by the referees in the World Cup.

They saw just what can happen in Thursday's opener, when Brazil beat Croatia 3-1 with the help of a debated call by referee Yuichi Nishimura of Japan.

It was on the Americans' minds Friday as they prepared to depart from their Sao Paulo headquarters for Natal. They play their Group G opener Monday night against Ghana, which eliminated the U.S. the past two World Cups.

Midfielder Jermaine Jones says he especially must be careful considering his penchant for yellow cards.