The 20-time grand slam champion is playing in his first tournament since November's ATP Finals and faced a battle to make the Melbourne major due to a back problem.
But Nadal has made the fourth round without dropping a set, seeing off Cameron Norrie 7-5 6-2 7-5 on Saturday.
"I did things well, [then there are] things that I need to improve. Something normal," the Spaniard said. "But, yes, happy, of course. Second week, straight sets. Can't complain."
PAIN RELIEF AT LAST FOR RAFA
Nadal might have been similarly dominant in his prior matches but revealed after beating Norrie he is only now feeling fitter.
"No, the back was not getting better each day; it was getting better today," he said. "But today is better, yeah, the first day I feel an improvement, and that's the most important thing for me today, more than any other thing.
"Of course, I was not serving my normal serve for the last 15 days. Today is the first day that I started to serve again my normal serve.
"But yesterday I didn't practice, so today was just warming up with the new, normal movement.
"So, of course, I didn't serve bad, but I can do better, I think. And I'm looking forward to doing it better. It has been an important victory for me.
"The biggest victory is the back is better for the first day. That's the most important thing."
Nadal will face Fabio Fognini next after he ended Australia's interest in the home grand slam with a 6-4 6-3 6-4 victory over Alex De Minaur, the host nation's final hope.
"It's one of those matches," an impressed De Minaur said. "You're out there leaving it all out there, but you can just feel that he's playing at another level."
MOODY MEDVEDEV MAKES AMENDS
There are three Russian men in the last 16 for the first time in Melbourne in the Open Era, but the country's biggest name survived a major scare.
Daniil Medvedev was cruising after taking the first two sets against Filip Krajinovic, only to drop the next two and engage in an angry back-and-forth with coach Gilles Cervara.
Cervara eventually left Medvedev's box as the fourth seed trailed 4-1 in the fourth set and did not return, but the 25-year-old recovered to get the job done in dominant fashion, a 6-3 6-3 4-6 3-6 6-0 victor.
Medvedev, with Mackenzie McDonald next, said of the incident with Cervara: "He said just before leaving that he's sure I'm going to win the match, but he's going to leave to let me be more calm.
"Sometimes maybe I will disagree but this time for sure it was a good thing to do.
"Today it helped, and definitely we're going to talk about it a little bit, but there is not a big deal."
Andrey Rublev joined Medvedev and compatriot Aslan Karatsev in the fourth round as he improved to 7-0 for the year with a three-set defeat of Feliciano Lopez. He will play Casper Ruud.
HISTORY CHANNEL OVER CHAMP
Defending champion Novak Djokovic's struggles with injury on Friday might have intrigued much of the tennis public, but Stefanos Tsitsipas was not overly concerned.
The fifth seed, who breezed past Mikael Ymer, did not watch the match and revealed he has little interest in keeping up with the exploits of his rivals.
"I might watch [Djokovic and Nadal] a little bit on TV if it happens that the TV is on or the right channel is on," he said. "Otherwise I just switch to History Channel.
"Definitely not tennis history. I think I have enough of tennis being in here every single day."
Tsitsipas will next play Matteo Berrettini, who is enjoying his best run at the Australian Open and saw off a side complaint to advance in three sets by edging Karen Khachanov, another Russian, in a trio of tie-breakers.