The Spanish top seed crushed Bolivia's Hugo Dellien at Melbourne Park, 6-2, 6-3, 6-0.

It continues the 33-year-old's quest for a 20th grand slam singles title, and a second in Australia after his 2009 triumph.

Dellien was Nadal's practice partner as a 17-year-old at the 2011 French Open, the grand slam the Spaniard has won 12 times to earn himself the nickname the King of Clay.

He is now the first Bolivian to have played at the Australian Open, but Nadal blew him away.

"He's a fighter, he has a great story behind him," said Nadal, who would draw level with Swiss legend Roger Federer if he claimed his 20th grand slam.

"I'm happy for him that he's playing at a very high level. 

"It's a positive start for me here. 

"What you want in the first round is just to win, and if it's in straight sets, it's better."

Elsewhere in the men's draw, Russia's fourth seed Daniil Medvedev needed four sets to beat American Frances Tiafoe.

The US Open finalist eventually came through 6-3, 4-6, 6-4, 6-2.

Austria's fifth seed Dominic Thiem knocked out Adrian Mannarino of France 6-3, 7-5, 6-2 and Germany's seventh seed Alexander Zverev ousted Italy's Marco Cecchinato 6-4, 7-6, 6-3.

There was joy for a pair of home Australians as Nick Kyrgios, seeded 23rd, defeated Lorenzo Sonego of Italy 6-2, 7-6, 7-6.

Alexei Popyrin went through against 28th seed Jo-Wilfried Tsonga, the 2008 finalist, after the Frenchman retired with a back injury.

Twelfth seed Fabio Fognini came from two sets down to beat American Reilly Opelka 3-6, 6-7, 6-4, 6-3, 7-6 in a bad-tempered affair, which saw the US player clash with the umpire and the Italian smash his racket. 

Canada's 20th seed Félix Auger-Aliassime was the highest-ranked player to exit, losing to Latvia's Ernests Gulbis 7-5, 4-6, 7-6, 6-4.

In the women's draw, Russian wildcard Maria Sharapova, the 2008 champion, lost 6-3, 6-4 to Croatia's 19th seed Donna Vekić.

"It's tough for me to tell what's going to happen in 12 months' time," said five-time Grand Slam champion Sharapova, who admitted she might not return to Melbourne. 

"I just don't know. 

"I haven't thought of my schedule moving forward from here yet." 

Czech second seed Karolína Plíšková won her clash with France's Kristina Mladenovic 6-1, 7-5, and Germany's 2016 champion Angelique Kerber, seeded 16th, saw off Italy's Elisabetta Cocciaretto 6-2, 6-2.

Romania's Wimbledon champion Simona Halep, the fourth seed, beat American Jennifer Brady 7-6, 6-1, while Swiss fifth seed Belinda Bencic got past Slovakia's Anna Karolína Schmiedlová 6-3, 7-5.

Britain's 12th seed Johanna Konta was the biggest casualty of the day, going down 6-4, 6-2 to Ons Jabeur of Tunisia.

Australia's Ajla Tomljanović knocked out Latvia's 31st seed Anastasija Sevastova, 6-1, 6-1.