Well this is interesting. Petra Kvitova hammers an ace on match point to finish off Aryna Sabalenka, 7-5, 3-6, 6-3. Sabalenka wanted to challenge the call, but she had none left. Naturally she had a hard time coming to grips with this reality, but them's the rules.
According to our friends on site, Hawk-Eye revealed that the serve was actually out (not that at matters, because #NoChallengesRemaining).