Serena was tired after Halep game, she had less then 24 hour between quarter-final and semi-final, that is why Pliskova won, maybe pliskova would have won also, but at least 3 sets if Serena had more time to recover but indeed "if you beat Serena in a GS this season, you win a GS this season" would confirm some kind of rule, but Serena not be beaten in Final here =), so I think new number 1 will take another GS this year