"Despite winning our last match, I faced two match points and barely got through that one, 7-6 in the third.
But all the players play the summer circuits, so they're used to it", he said.
"I don't know 100 percent about what's going on or not, but at some point is good that the players speak between each other about what we want or what we don't want", said Nadal.
The temperature had dropped to 29 C (84 F) by the time defending champion Roger Federer wrapped up his 6-4, 6-4, 7-6 (4) win over Jan-Lennard Struff just after 11:30 p.m. on Rod Laver Arena. "She played very good the last two here".
The heat was intensifying earlier when six-time champion Novak Djokovic extended his personal streak against Gael Monfils to 15-0 with a 4-6, 6-3, 6-1, 6-3 victory in which both players slouched over in the shade at the back of the court between points. I did my job in two sets against someone that's been troubling in the past for me.
"We're high-level athletes capable of pushing the limits very far and sometimes too far, that's why I say that it could be unsafe". "I'm exhausted and dizzy".
Kerber had a standout 2016 when she won in Australia, beating Serena Williams in the final, to become the first German since Steffi Graf in 1999 to claim a Grand Slam.
Halep said she is still troubled by a twisted ankle sustained in her first match against Destanee Aiava, but the top seed defied the pain to stay in the hunt for a first major title. "I think this limit should be a little bit lower", Cornet told reporters. "I mean, they're struggling some way or another".
Stan Wawrinka, the 2014 Australian Open champion, No. 7 David Goffin and No. 13 Sam Querrey didn't make it through the second round. "I understand there is a factor of tickets". You have to take into consideration different angles before making a big call like that.
The former world number one, who missed last year's tournament because of her ban for the use of a banned substance, takes on the Latvian 14th seed in the first match on the main showcourt so should escape the worst of the heat.
No 3-ranked Muguruza was the highest-ranked player to fall so far, but follows Venus Williams and US Open champion Sloane Stephens out of the tournament in the first week. "Not easy mentally, but from when I was a break up in the third set, the mind was again positive".
At 4-4 a backhand victor got Sharapova to break point and when a second screamer followed it was greeted by a double-fist pump from the Russian.
Also advancing were No 8 Caroline Garcia, who beat Marketa Vondrousova 6-7 (3), 6-2, 8-6, and No 26 Agnieszka Radwanska, who next plays Hsieh.
Ninth seed Johanna Konta tumbled out of the second round in blazing sunshine and windy conditions after a defeat by world No. 123 Bernarda Pera.
No 21 Albert Ramos beat another American, wildcard entry Tim Smyczek 6-4, 6-2, 7-6 (2).