Two of them will meet in the third round.
The crowd sang Happy Birthday and gave three hoorays to celebrate Kerbers 30th birthday.
Zverev won five titles past year, including Masters 1000 titles at Rome and Montreal.
After current ATP player council president Novak Djokovic reportedly held a players-only meeting ahead of the Melbourne event, Federer said that there's "no doubt" the slams could raise the prize money on offer.
"It was obvious we both suffered on the court today", Djokovic said. Really tough conditions brutal..
Temperatures are only expected to rise on Friday, as Grigor Dmitrov takes to the court.
Sevastova's tricky game wore Sharapova down at Flushing Meadows and the 2008 champion appeared determined not to let that happen again, blasting her way to the first set in just 23 minutes. I did my job in two sets against someone that's been troubling in the past for me. Was pretty hot. I thought I was very good.
Djokovic looked far from his best but was still too good for the enigmatic world No.39, maintaining his flawless record against Monfils with a 4-6 6-3 6-1 6-3 victory.
Scorching temperatures are common at the Australian Open - so much so the tournament has an extreme heat policy that allows for the referee to close the roofs on the three main show courts and suspend play on the outer courts when temperatures surpass 40 Celsius. "If you don't play matches, people will be unhappy".
"At the end of every Australian Open we always review our policies and procedures and consult with all stakeholders".
Federer, who has amassed nearly $112 million in career prizemoney, supported Djokovic's push for a bigger percentage of revenue for players.
The Spaniard had a troubled preparation for the tournament, retiring with cramps in the second round at the Brisbane International and withdrew before her quarterfinal at Sydney because of a right thigh injury. But she made a meal of it against local hope Destanee Aiava.
Another seed to make an early exit was ninth seed Johanna Konta, who was shocked by lucky loser Bernarda Pera of the US. I was checking the tickets to fly back. "I'm happy I didn't buy one". She was also aggressive on return, which paid dividends for the Russian as she was able to break twice in the opening set before taking it 6-1.
Also advancing were No. 8 Caroline Garcia and No. 26 Agnieszka Radwanska, who next plays Hsieh. Elsewhere in the third round, top-seeded Simona Halep plays American Lauren Davis.
Former No. 1-ranked Karolina Pliskova advanced to a third-round match against No. 29 Lucie Safarova.
Elena Vesnina became the 10th of the top 16 women's seeds to go out by the second round, losing 7-6 (7-4) 6-2 to Japanese 20-year-old Naomi Osaka.