Djokovic, the world number one who is seeking a seventh Australian Open crown, won a repeat of the 2008 final as he beat Frenchman Jo-Wilfried Tsonga 6-3, 7-5, 6-4 on Rod Laver Arena in Melbourne.

The 31-year-old Serbian, a 14-time Grand Slam champion, will next face 25th seed Denis Shapovalov of Canada.

While Djokovic was largely untroubled by Tsonga, Halep, the women's world number one, survived a scare in her encounter with American Sofia Kenin.

The Romanian looked on course to record a comfortable victory before she dropped the second set and then was broken in the third.

Halep, last year's runner-up, eventually clinched a battling 6-3, 6-7, 6-4 win to set up a meeting with American veteran Venus Williams.

"I have no idea how I won," said Halep, who said she suffered a slight injury during the second set.

"It was difficult to stay in there for every ball and run so much.

"But I just fought because I wanted to win."

American Serena Williams continued her pursuit of a record-equalling 24th Grand Slam crown as she confidently dispatched Canada's Eugenie Bouchard.

The 37-year-old, a seven-time champion in Melbourne, overcame Bouchard 6-2, 6-2.

Dayana Yastremska, ranked 57th in the world, faces Williams in the next round and will be tasked with beating a player many consider to be the favourite for the title.

Alexander Zverev, the fourth seed, was another player who struggled before securing a place in the third round.

The highly-rated German held off a valiant fightback from Jeremy Chardy of France to seal a 7-6, 6-4, 5-7, 6-7, 6-1 win.

Britain's Johanna Konta and Spain's Garbiñe Muguruza then made unwanted history as they took to the court at 12.30am local time, the latest time a match has ever started at the season's opening Grand Slam.

Muguruza eventually prevailed 6-4, 6-7, 7-5 in a match which finished beyond 3am local time.