Leading 4-0 in the first set and looking every inch the short-priced favourite to go on and claim her sixth title at Melbourne Park, Williams slid, rolled over the top of her right ankle, then lay motionless on the bright blue court.
Television cameras immediately flashed to her mother, Oracene Price, who let her normally stoic countenance slip for an instant with a flicker of concern.
If Williams' spill gave Gallovits-Hall hope of an upset, the American quickly snuffed it out.
After gingerly walking off court to have her ankle re-taped, Williams proceeded to pummel the Romanian, recording a 6-0 6-0 'double bagel' win in 54 minutes, eight of which were taken up by the injury break.
The incident brought back bad memories for Williams, who rolled her left ankle at the Brisbane tournament last year and was then upset by world number 56 Ekaterina Makarova in the fourth round at the Australian Open.
Williams said her first thought as she lay on Hisense Arena on Tuesday was: "Oh, not again".
"I just think that I was definitely a little bit in shock and I was thinking, 'I hope it's not as serious', because it was really serious last year."
While Williams recovered enough to get through the match, the real test will come over the next two to three days, when the ankle could continue to swell and cause more pain.
An indication of the seriousness of the injury could come on Wednesday when she is due to partner sister Venus in the first round of the doubles against Italy's Camila Giorgi and Switzerland's Stefanie Voegele.
"Obviously there's pain. Obviously there's swelling. So it's going to be really important to see how the next few hours unfold," she added.
"Unless something fatal happens to me, (and) I hope not, I'm going to be on the doubles court.
"I'm not here to make excuses, I'm here to play."
Williams, who has won the last two Grand Slams, got through the match against the world No. 110 by swinging away and trying to limit her movement as much as possible.
She is unlikely to enjoy the same luxury against the world's top players deeper in the draw.
The 31-year-old realises her window to add to her 15 Grand Slam singles titles is narrowing.
"I have a day to work on it. At this point it's not a lot of time," she added. "But I'm not 18-years-old where I want to sit this one out or I don't have to run to the forehand.
"I'll be out there. I mean, unless something fatal happens to me, there's no way I'm not going to be competing.
"I'm alive. My heart is beating. I'll be fine."
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