Schmiedlova, a 19-year-old Slovak who had never even taken a set off of a Top 30 player beforehand, rallied from a set and a break down to beat a No.29-seeded Venus Williams, 2-6, 6-3, 6-4, showing off some impressive tenacity in the second and third sets, as well as an absolute dynamite backhand - in fact she finished the two-hour, 14-minute match off with a massive crosscourt backhand winner.
"She played really well, even the first set, she was competitive," Venus said. "In the second and third sets I made too many errors, and she played so well and kept getting so many balls in the court.
"She's going to be even better as she continues to play. I see wonderful things for her."
The other match was no contest - Muguruza was totally dialed in while Serena Williams was completely off her game, eight winners being far outweighed by a whopping 29 unforced errors. After 64 minutes, Muguruza, a powerful 20-year-old Spaniard, had pulled off the upset of the tournament, 6-2, 6-2.
"Since I was a child, when I turned on the TV, I've seen her play," Muguruza said. "For everything when I'm practicing, I'm like, 'Okay, how does Serena serve? How does she play a backhand?' I've seen like 100 videos of her. So it was really difficult to stay calm and think I'm playing just another player."
The World No.1 was asked how she felt about her season. "My first few months haven't been great at all," she said. "I haven't gotten past the fourth round of a Grand Slam this year. I have a couple of words to describe it, but I think that would be really appropriate, so I'm going to leave it at that.
"I love it here, but there's always next year. At least I won't have any points to defend."
And the upsets didn't stop there: Johanna Larsson carved out a 5-7, 6-4, 6-2 win over No.12 seed Flavia Pennetta, Mona Barthel got past No.16 seed Sabine Lisicki, 6-1, 3-0, when the German had to retire with a right wrist injury, American wildcard Taylor Townsend outlasted No.20 seed Alizé Cornet, 6-4, 4-6, 6-4, and Ajla Tomljanovic picked off No.32 seed Elena Vesnina in straights, 7-6(6), 6-2.
All the other seeds moved on, though - No.3 seed Agnieszka Radwanska, No.7 seed Maria Sharapova, No.8 seed Angelique Kerber, No.9 seed Dominika Cibulkova, No.14 seed Carla Suárez Navarro, No.18 seed Eugenie Bouchard, No.19 seed Samantha Stosur and No.31 seed Daniela Hantuchova.
Sharapova rallied from an early break down in the first set and ended up getting past the always-dangerous Tsvetana Pironkova in straight sets, 7-5, 6-2. And all the upsets haven't changed her.
"You always have to follow your path and always concentrate on your work and who's ahead of you, and not get worried about what's going on," the four-time Grand Slam champion said. "Obviously when you go on court you're aware of a lot of the upsets, not just in the women's but in the men's, as well.
"So it's great to get a win in that type of atmosphere."