Well, she has been undefeated on hard this year and I so wish it would continue to stay that way, but I have a feeling Keys will take that match easily. Kaias exhaustion was already obvious in last match, Kasatkina lost because Kaia just wanted to win it more. Kaia had lots of UE, but also decent amount of winners....she was so up and down...she even choked, like on her best days, but then pulled herself together again.
If she can make her serve work, then it is one of the bests in womens tennis.
Right now I am not even sure what her playing style is. She herself said she is just so freaking happy, she can´t stop smiling, being in QF so soon after comeback, every win after qualies have been bonus. She said having no target, no expectations, nothing to prove is the best way to play tennis...
So...she will probably lose to Keys today...but I would still put my money on Kaia, just in case!