Those playing on Friday seemed to cope better despite marginally hotter temperatures, although France's Alize Cornet needed treatment after lying down on the court in her defeat by Elise Mertens.
Earlier in the day, Lauren Davis recovered from a set down against Andrea Petkovic to book her spot in the third round - final score, 4-6 6-0 6-0.
"The conditions of play are established prior to the event, and this includes the Extreme Heat Policy (EHP)".
"The limit of not playing the match is really high, it's like it needs to be above 45 degrees and humidity".
"The crowd was in the shade but for the player it's incredibly tough". "I think this limit should be a little lower because playing in this condition is not nice for anyone".
She said players' determination to fight on regardless was part of the problem, given they might not know their limits and continue to push themselves into risky territory.
"But I agree that sometimes it can be too much and the high level athletes are capable of pushing these limits very far, sometimes too far and that's why I say it could be risky".
Monfils claimed he had put his health at risk by remaining on court and urged players not to feel ashamed to walk off court if they felt similarly affected.
The tournament's extreme heat policy calls for the roofs to be closed on the main show courts and play to be suspended on outer courts when the temperature reaches 40 degrees Celsius (104 Fahrenheit) and the wet-bulb globe temperature (WBGT), which takes into account humidity and wind speed, reaches 32.5 Celsius (90.5 Fahrenheit).
Organisers defended the decision to allow play to continue on Friday.
"We had our weather experts from the Bureau of Meteorology regularly providing updates on the temperature and the timing of the forecast cool change".
All Offers and Promotions posted in this article excludes NSW residents.