Defending champions Madison Keys and Jannik Sinner are both safely through to the Australian Open second round, but it was the Italian who enjoyed a far more comfortable opening match at this year's tournament.
While American Keys recovered from a nightmare start on her way to victory over Oleksandra Oliynykova, Sinner powered to a two-set advantage before opponent Hugo Gaston suddenly retired in tears on his chair due to illness.
Keys secured her first Grand Slam crown when she defeated world No 1 Aryna Sabalenka in last year's final but began her title defence in nervy fashion.
Oliynykova, making her Grand Slam main draw debut while also taking on a top-50 opponent for the first time, stormed into a 4-0 lead before Keys battled back to 4-4.
The Ukrainian would show her own fighting spirit, though, taking the opener into a tiebreak where she established 5-2 and 6-4 leads but could not press home the advantage.
Keys held off two set points before going on to snatch the tiebreak 8-6, celebrating her big escape with a mighty roar after a marathon 72-minute tussle.
The 30-year-old admitted to “playing a little timid and not really trusting my first instinct” as she struggled with nerves making 30 unforced errors in the opening set.
There were no such problems in the second which Keys blazed through in 28 minutes, with just seven unforced errors and losing only 12 points, to complete a 7-6, 6-1 victory and set up a second-round match with countrywoman Ashlyn Krueger.
“I've been thinking about this moment for basically a year,” said ninth seed Keys. “The moment they say, 'Ready, play', it all hits you in a way that I don't think you can ever really explain.
“As nerve-racking and stressful as that can be, I'm still reminding myself of just how few people get to be in that moment.
“Being able to walk out today and have the crowd be as welcoming as they were, I'll take the stress any day.”
Meanwhile, Sinner's attempt to seal a third consecutive Melbourne title began in unexpectedly quick fashion following the retirement of Gaston.
The world No 2 – who defeated Daniil Medvedev and Alexander Zverev to claim the last two titles Down Under – looked in imperious form as he surged into a 6-2, 6-1 advantage at Rod Laver Arena.
But after losing the second set, Gaston gestured he could no longer continue and was left in tears on his seat before the Frenchman slowly made his way off court, applauded by Sinner as he went.
“I saw that he was not serving with a very high pace, especially in the second set,” Sinner said of his opponent.
“It's not the way you want to win the match. He's such a talented player, he has such incredible touch and moves very well. I knew that I had to play high-level tennis and try to be as aggressive as possible, which I've done so I'm very happy.
“I'm happy to be back here, it's a very special place for me. The atmosphere as always was amazing.
“I felt very well-prepared, we worked a lot physically and also on the court too. The official matches are always very different so I'm very happy with how I started.
“Obviously a bit of tension but now it's time to enjoy – all the hard work is done and we practice for moments like this, so I'm very happy to be back here.”
Elsewhere in the women's draw, reigning WTA Finals champion Elena Rybakina beat world No 100 Kaja Juvan 6-4, 6-3 in 72 minutes at the Margaret Court Arena.
Switzerland's Belinda Bencic swept aside Briton's Katie Boulter 6-0, 7-5 with the first set lasting just 26 minutes. The 10th seed's win streak now stands at 12 matches, matching her career best.
Boulter did produce a fightback in the second but reigning Abu Dhabi Open champion Bencic came up with a composed performance as she hunts for a first Grand Slam title.
Janice Tjen became the first Indonesian to win a match at the Australian Open in 28 years when she beat 22nd seed and former US Open runner-up Leylah Fernandez 6-2, 7-6.
American duo Ben Shelton and Taylor Fritz – seeded eight and nine in the men's draw – are both through to the next round after defeating French opposition.
Shelton – lost to Sinner in last year's semi-finals – overcame Ugo Humbert 6-3, 7-6, 7-6 while Fritz needed four sets to dispose of Valentin Royer 7-6, 5-7, 6-1, 6-3.
