Temperatures on day five reached 40C in Melbourne while six-time champion Novak Djokovic called conditions "brutal" and "right on the limit" on Thursday .
Officials said they "came close" to enforcing their heat rule on Friday which would have halted play.
Director Craig Tiley said: "We are, at the end of the day, an outdoor event."
He added: "We want it to stay an outdoor event as long as possible but at the same time ensuring that the health and wellbeing of players is taken care of."