Japan's Naomi Osaka hits a return against Ukraine's Elina Svitolina during their women's singles match on day four of the 2016 Australian Open tennis tournament in Melbourne on January 21, 2016. AFP PHOTO / SAEED KHAN-- IMAGE RESTRICTED TO EDITORIAL USE - STRICTLY NO COMMERCIAL USE / AFP / SAEED KHAN (Photo credit should read SAEED KHAN/AFP/Getty Images)

Serena Williams and Naomi Osaka have cruised through their opening round matches on day 1 of the Australian Open.

Osaka registered the first win of the tournament as she defeated Anastasia Pavlyuchenkova in straight sets 6-1, 6-2.

Serena Williams also won with ease as she smashed unseeded Laura Siegemund in just 56 minutes, 6-1, 6-1.

Serena was joined in the winners circle by sister Venus who defeated Kirsten Flipkens in straight sets also.

Serena praised her sister after their wins.

“She’s such an inspiration because she never gets frustrated about her situation, health-wise. She’s always looking on the bright side. Then she works so hard. Yeah, she’s been great,” she said.

Williams was diagnosed with Sjogren’s disease in 2011. She switched to a vegan diet to combat the illness.

“It was so good to train with her. It was so good every day,” added Serena.

“It’s also very inspiring because she still pushes me on a level that no one’s able to push me, so it was incredibly helpful.”

2016 champion Angelique Kerber was upset on the opening day of the Grand Slam as she bowed out.

The 23rd seed was beaten 6-0, 6-4 and blamed the hard lockdown she had to undertake for her early exit.

“I was really trying to staying positive and doing the best out of the two-week situation but, of course, you feel it, especially if you play a real match where it counts and you play the first matches in a Grand Slam, also against an opponent who doesn’t stay in the hard lockdown.”

“When I’m looking back, of course I was not planned, the two weeks hard quarantine.

“I don’t know, maybe if I knew that before to stay really two weeks in the hard quarantine without hitting a ball, maybe I would think twice about that (coming to Melbourne).

“But I was trying to take the motivation also for this tournament because it’s one of my favorite tournaments.

“Of course, I knew that we play with a little bit of fans,which is always such a different than playing with no fans.

“It makes tennis playing much more fun to play out there. So that was my motivation.

“But, of course, if I knew the real situation before my trip, I would think maybe twice to come here.”

On the men’s side of the draw Stan Wawrinka went through in straight sets while Australian fan favourite John Millman bowed out in a five set classic.

Millman fell too French 21-year-old Corentin Moutet in a game that had it all, it was full of highlights but ultimately saw the local hope bow out.

Moutet had moments where he looked likely to implode, he argued with crowd and broke a racquet before composing himself to claim an iconic victory.

Nick Kyrgios and Novak Djokovic kick-off their campaigns on night one.