Barty overcame a stumbling start to claim a 6-2 6-4 victory over Ekaterina Alexandrova at an empty Margaret Court Arena on Saturday.
The 24-year-old would have expected the backing of a fiercely partisan crowd for a weekend evening match at her home Grand Slam, but Melbourne's five-day lockdown left her playing in front of officials, ballkids and coaches.
While most other players have seen plenty of empty courts on the WTA tour over the last year, it was a new experience for Barty, who elected to stay home while the COVID-19 pandemic raged around the world.
"It's very strange, I've never experienced it before in my life," she said. "It changes the sound of the court. Bit rude but I like it. I love the crowd but I loved the sound of the ball."
The top seed was broken in her first service game but quickly rallied to take the first set when the Russian slapped the ball into the net for her 16th unforced error.
Barty was all over Alexandrova's serve from the start, but some of her shot selection was questionable as she tried to finish off points, particularly some ill-judged lobs.
Showing no signs of being hampered by her heavily strapped left thigh, the Australian battled back after being broken again in the second set and secured the victory with a fifth and final break of serve.
Barty said she had been happy with how effective her slice backhand had been, although she conceded that she possibly went to it too often.
"I've never played with her before and never hit with her before," she said of her opponent.
"I just had to figure out where I wanted to place the ball and change my patterns, but I was happy with the run I was able to get on."
Barty, who is looking to become the first homegrown Australian Open singles champion since 1978, will play American Shelby Rogers for a place in the quarter-finals.
Nadal overcame some stiff early resistance from Britain's Cameron Norrie before easing into the fourth round with a 7-5 6-2 7-5 victory on Saturday.
After being heckled by a loud-mouthed fan in his previous round win against Michael Mmoh, Nadal enjoyed an incident-free evening in an empty Rod Laver Arena to reach the round of 16 at a Grand Slam for the 49th time in his career.
The 34-year-old Nadal, bidding to claim a record 21st Grand Slam title, will face Italian Fabio Fognini next.
Nadal won the opening six points, but 69th-ranked Norrie was not intimidated in his first meeting with the Spaniard and claimed the first break of the match to lead 3-2.
He was immediately broken to love though and folded at 5-6 to drop serve again and hand Nadal the first set in 48 minutes.
Thereafter it was a routine day at the office for Nadal, who dominated without ever needing to find top gear, showing no sign of the lower back injury that dogged him in the warmup.
"All the matches are tough, he came here winning a couple of very good matches. I didn't convert the opportunities I had early in each set so the situation became a bit more difficult," Nadal, who is yet to drop a set, said.
"I'm happy, I had a few good feelings, of course I have to keep improving and tomorrow is another day to practice but into the second week and that's the main thing for me."
Nadal's only title in Melbourne was in 2009 but with eight-time champion Nova Djokovic suffering an injury in his third-round win over Taylor Fritz the Mallorcan might not ever have a better chance to double his tally.
He was not at his dazzling best against Norrie in a eerily flat atmosphere, a result of Melbourne's five-day COVID lockdown forcing organisers to close the doors to fans.
But it was enough to post a 16th successive win against a fellow left-hander - a run stretching back to 2017.
A bigger test awaits on Monday when Fognini, who dispatched Australian Alex de Minaur in straight sets on Saturday.
"We've played a lot of times and he has beaten me before," Nadal said. "He will be hungry to play well and has had a very impressive win today so he will come with plenty of confidence.
"You don't expect an easy round in the round of 16 so it will be tough and I have to be ready for it."