The top seed entered Rod Laver Arena with a frown and grumbled through an hour of miscued groundstrokes, but she was all smiles as she approached the net to commiserate the 26th-seeded Ukrainian after doling out a third set bagel.
"Nowadays, if I get past the fourth round, it's like party time," Williams told reporters breezily.
It was not long before the 18-times grand slam champion turned her attention to avenging one of her bigger upsets at the majors.
Spaniard Muguruza was a fast rising if unheralded 20-year-old before Roland Garros last year but became an overnight sensation by thrashing a lead-footed Williams 6-2 6-2 in the second round on the way to a maiden grand slam quarter-final appearance.
Muguruza, seeded 24th in Melbourne, has continued her upward trajectory and like Williams bageled her third round opponent, Timea Bacsinszky, in the third set of their match on Saturday.
Williams described her French Open shock as a "good loss".
"As angry as I was, it was the best loss I had the whole year last year," she said.
"Had a lot of them. But that one in particular made me realise what I needed to work on. It opened my eyes towards a lot of things.
"I was like, 'oh my gosh, if I don't change, then I'm going to be forever in the same position.' It actually ended up helping me a lot."
Roger Federer's stunning upset by 46th-ranked Italian Andreas Seppi in the third round on Friday was also a reminder for the world number one to be on her guard.
Muguruza picked Williams apart in Paris by consistently attacking the American down the middle of the court and said she would relish the prospect of another showdown.
"That day I played really good," she said of the French Open clash. "I did what me and my coach were talking to do on the match. Everything was perfect.
"That's why I could win that match. You never have these kind of matches usually when you play perfect, so just hoping to try to do the same.
"Eventually I will have to play against her again, so I think I don't have anything to lose. I don't think I have pressure. I like to play big matches in centre courts."
(Editing by Peter Rutherford)
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