Melbourne (AFP) - Nature-lover Novak Djokovic strolled into the Australian Open third round on Thursday as an erratic Madison Keys wobbled but did enough to keep her title defence on track.

Men’s title-holder Jannik Sinner is also in action later on day five at a sunny but cooler Melbourne Park.

Djokovic sent 141st-ranked qualifier Francesco Maestrelli packing in straight sets at Rod Laver Arena.

The Serbian great is on his latest mission to win a record 25th Grand Slam title and dismissed the Italian 6-3, 6-2, 6-2.

Djokovic faces China’s Shang Juncheng or Botic van de Zandschulp of the Netherlands next.

Djokovic is well known for his sometimes unusual preparations, which include hugging a Brazilian fig tree in Melbourne’s botanical gardens.

“That is my oldest friend here in Melbourne,” said the 38-year-old former world number one, who has won 10 Australian titles, more than anyone in history.

“He has been there to heal my wounds and give me company.

“We have a friendship going over 20 years.”

Keys blew hot and cold before getting over the line 6-1, 7-5 against fellow American Ashlyn Krueger.

Keys, who upset Aryna Sabalenka in last year’s final, admitted after her laboured first-round win that she was a bundle of nerves and “too timid”.

The 29-year-old threw off the shackles in the first set against the 92nd-ranked Krueger, taking it in just 23 minutes on John Cain Arena before having to rally from 2-5 in the second.

“I started really well and Ash a little slowly,” said Keys, who began her season with quarter-final exits at Brisbane and Adelaide.

“I fully expected her to raise her level and she did. It got away from me a bit.”

She meets the experienced Karolina Pliskova of the Czech Republic next.

In another all-United States clash, the sixth seed Jessica Pegula made light work of her doubles partner McCartney Kessler in a rapid 6-0, 6-2 win.

Another ruthless winner was fourth-seeded American Amanda Anisimova – 6-1, 6-4 against the Czech Katerina Siniakova.

But 25th seed Paula Badosa of Spain, who lost to Sabalenka in the semi-finals a year ago, is out after being stunned 6-4, 6-4 by Russia’s 101st-ranked Oksana Selekhmeteva.

Second seed Iga Swiatek, who has won six major titles but never been successful in Melbourne, later faces Marie Bouzkova of the Czech Republic.

Two-time former champion Naomi Osaka, who made a grand entrance on Tuesday in a jellyfish-inspired outfit, plays Romania’s Sorana Cirstea.

Fifth seed Elena Rybakina of Kazakhstan will also be in second-round action.

- Sinner gets set -

The men’s seeds all went through untroubled.

Lorenzo Musetti, the fifth seed, beat fellow Italian Lorenzo Sonego 6-3, 6-3, 6-4.

American eighth seed Ben Shelton was a comfortable 6-3, 6-2, 6-2 victor over Australia’s Dane Sweeny.

Other winners in the men’s draw included 15th seed Karen Khachanov of Russia and 16th seed Jakub Mensik of the Czech Republic.

The 20-year-old Mensik eased past Rafael Jodar of Spain 6-2, 6-4, 6-4.

Sinner is attempting to win a third Australian Open in a row.

The Italian coasted through round one when his French opponent Hugo Gaston retired with Sinner in a commanding 6-2, 6-1 lead.

He will be strong favourite against the 88th-ranked Australian James Duckworth but will have to face down a partisan home crowd on Rod Laver Arena.