The 19-year-old Raducanu, playing in her first grand slam match since winning the US Open last year, stormed through the first set in just 17 minutes against Stephens, herself a US Open champion in 2017.
But the momentum swung in Stephens’ favor in the second set as the American broke Raducanu on three occasions to level Tuesday’s match.
Battling through some long rallies in the final set, Raducanu moved into a 5-0 lead and went on to wrap up the match just before midnight (8 a.m. ET) in Melbourne.
“Both me and Sloane really put everything out there and gave it all we had,” Great Britain’s Raducanu said during her on-court interview.
“I thought it was a really high-quality match with some very long rallies. I’m very happy to have come through against such a great champion like her.”
After her sensational triumph at the US Open last year, Raducanu endured a difficult run of results in October and November and said she was still “adapting to the fast-paced life of the tour.”
In December, she tested positive for Covid-19 ahead of an exhibition event in Abu Dhabi and returned to action in Sydney earlier this month.
Her next match at the Australian Open will be against Montenegro’s Danka Kovinic, with two-time grand slam champion Simona Halep a potential opponent in the third round.
Another British player, Andy Murray, also got off to a winning start on Tuesday as he outlasted Georgia’s Nikoloz Basilashvili 6-1 3-6 6-4 6-7 6-4.
Playing in his first Australian Open since 2019, Murray beat Basilashvili for the second time in the space of a week having also triumphed in Sydney in the build-up to the Australian Open.
This time, the three-time grand slam champion exhibited the same grit and resolve that has characterized Murray’s playing career.
“It’s been a tough, tough three, four years. Put in a lot of work to get back here,” said Murray, who considered retiring after the Australian Open three years ago before undergoing career-saving hip surgery.
“This is the one where I thought potentially I played my last match, but amazing to be back winning a five-set battle like that. Couldn’t ask for any more.”
Elsewhere in the men’s draw, second seed Daniil Medvedev, a finalist at last year’s tournament and arguably the favorite this year after Novak Djokovic’s withdrawal, defeated Henri Laaksonen 6-1 6-4 7-6.
There was also a straight-sets victory for home favorite Nick Kyrgios against Britain’s Liam Broady to set up a second-round clash against Medvedev.