Wearing a sleeveless top, he showed no signs of any issues against Duckworth. He returned the favor quickly, though, to seal his spot in the second round.
"It was good. It is normal that beginnings are tough, but every day helps and every day makes me feel better, makes me feel more confident", said Nadal, who limped out of both the Australian and US Opens previous year.
Maria Sharapova has the second-best record among active women's players in first-round matches at the majors, and she gave an illustration of why that's the case with a ruthless 6-0, 6-0 win over Harriet Dart.
He lost a five-setter to Britain's Kyle Edmund in round one a year ago and had to overcome a second-set blip Monday, dropping his serve twice from a break up against the French world number 41, before prevailing in two hours 53 minutes on Melbourne Arena.
Although she had a game point in the fifth game of the second set, she squandered that and all her other opportunities against the player she considers her idol.
The centre court humiliation had Dart weeping as she beat a hasty exit and Sharapova had little sympathy for the 22-year-old after her nightmare debut at Melbourne Park.
"I mean, there is no time for that, I'm sorry to say ... when you're playing the first round of a Grand Slam", she said.
Stung by a first-round loss at Wimbledon previous year, Sharapova said she couldn't afford to feel any empathy for Dart.
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"And, you know, trust that that's going to pay dividends for me in the future".
"I'm just excited. I think it's a positive to be here as the defending champion. I was glad that I did the right things from the beginning till the end".
There were also questions about the 2017 US Open winner's form coming into the tournament after poor performances this month at warm-ups in Brisbane and Sydney.
After having missed most of the 2018 season due to a foot injury, Nadal made a confident start at the Australian Open.
Katie Boulter earned the distinction of winning the first 10-point tiebreaker under the Australian Open's new system for deciding sets. She went on to beat Russia's Ekaterina Makarova 6-0, 4-6, 7-6 (10/6).
Nadal used all his experience to win his next service game from 15-30 down before breaking Duckworth again for the straight-sets win.
Wimbledon runner-up Kevin Anderson fired 14 aces and 47 winners to blast past Frenchman Adrian Mannarino 6-3 5-7 6-2 6-1.
Roger Federer and Caroline Wozniacki open their Australian Open title defences Monday as Andy Murray takes to the court for what could be his farewell match at Melbourne Park and potentially his last ever.