"It would go from 1 to 10 and I'm like at a 100 right now,” admitted Osaka, describing her levels of disappointment.
The Japanese star knew this time she had to start well. Serving first Osaka was stepping in and trying to be the frontrunner, but the radar was well off course.
On the other side of the net, Siniakova, ranked No.42 in singles, was providing a defensive masterclass.
Osaka saw three break chances vanish as Siniakova withstood the early pressure to take control of proceedings. The top seed fended off a brace of break points at 4-4 with two cannonball forehands, but a flurry of errors unravelled that work.
Siniakova slipped to 0-40 serving for the set, before dinking a deft drop shot over as the catalyst to head to the changeover halfway to claiming a maiden fourth round at a major.
“I was trying to keep her behind the baseline as much as possible and trying to just put so many balls in and just don't give her easy points,” reflected the 23-year-old Siniakova.
“I think it was one shot I could use against her, and it was brave, but I believe in my dropshot. I think it's really good. Actually, it was tough to finish the set, and I was really happy I fight back and I finish it.”