MELBOURNE, Australia -- Novak Djokovic and Aryna Sabalenka launched their title defenses on Sunday with contrasting victories on day one of the Australian Open.

Djokovic was the headline act as the first Grand Slam of the year, which runs through to January 28, started in Melbourne a day earlier than usual in a bid to ease concerns over late finishes that had plagued the event.

The world No. 1 was left relieved after surviving an unexpected four-hour thriller against qualifier Dino Prizmic with a 6-2, 6-7 (5), 6-3, 6-4 win.

The 36-year-old was well below his best, but still recorded his 29th straight victory at his favored event. Djokovic will play Alexei Popyrin or wildcard Marc Polmans in the second round.

The Serbian is gunning for an unprecedented 11th title at Melbourne Park and a record-extending 25th Grand Slam crown.

"It could easily have been his match as well," Djokovic said of Croatia's Prizmic. "He showed great mentality and resilience. He really made me run for my money tonight."

Fifth seed Andrey Rublev also survived a major scare against Brazil's Thiago Seyboth Wild after being pushed to the brink having relinquished a two-sets-to-love lead.

The Russian appeared set for a shock early exit when he trailed 4-1 in the fifth set tiebreak, but Rublev dug deep to prevail 7-5, 6-4, 3-6, 4-6, 7-6 (10-6). He sealed the match with an ace then collapsed to the court and unleashed a triumphant roar to underline his relief.

"When I was losing 4-1, mentally I gave up and maybe that's what helped me in the end," Rublev said. "I felt it's not my day, but then I hit some good serves and good returns."

Fourth seed Jannik Sinner made a rusty start in his first match of the year, but still came away with a straight sets win over Dutchman Botic van de Zandschulp.

In his first match since leading Italy to last year's Davis Cup title, Sinner overcame struggles on his forehand before claiming a 6-4, 7-5, 6-3 victory in two hours and 34 minutes.

Sinner is deemed as a challenger to favorites Djokovic and Carlos Alcaraz having beaten them both last season.

"It's never easy playing the first match of the season, so I'm happy to get the win and now I have two days of practice to get better," he said.

Women's second seed Sabalenka crushed Germany's Ella Seidel 6-0, 6-1. The match started on Rod Laver Arena at close to midnight, but Sabalenka sped through proceedings to wrap up an almost flawless performance in 53 minutes.

Eighth seed Maria Sakkari swept aside Japan's Nao Hibino in straight sets, while former Australian Open champion Caroline Wozniacki advanced to the second round after 20th seed Magda Linette retired through injury.

It was a disappointing opening day for China's two women's players in action.

30th seed Wang Xinyu was upset by Frenchwoman Diane Parry 6-3, 2-6, 6-3.

Rising Chinese women's star Bai Zhuoxuan was hampered by a leg injury before being knocked out 4-6, 7-5, 6-2 to Elina Avanesyan of Russia.

21-year-old Bai started well and gained an early lead, but she became restricted in her movement as the match wore on.

The heavily bandaged Bai succumbed in a one-sided final set to lose in two hours and 27 minutes.

In day two action on Monday, two-time former Australian Open champion Naomi Osaka will make her Grand Slam return since becoming a mother when she plays 16th seed Caroline Garcia.

The highest-ranked Australian Alex de Minaur meets former world No. 3 Milos Raonic, while China's top men's player Zhang Zhizhen takes on Federico Coria of Argentina.