Some officials have been criticised for their perceived reluctance to use their cards regularly, but Boyce has insisted that there were no instructions from the sport's governing body on that subject prior to the tournament.
"I think the refereeing has been superb, and it has not happened by chance," FIFA's second in command told reporters.
"I have seen all the courses and seminars, listened to the instructors, and spoken to the referees and they have told me they have never had such good preparation for a World Cup.
"The referees have been told to only send a player off if they were 100 per cent certain it was a red card, but nothing has ever been said about being lenient."
There have been just 10 red cards shown ahead of the World Cup's final two matches, the lowest number of dismissals in the tournament since 1986.