Kerber beating Serena in Australia 2016, she was after her maiden win, up against the greatest of all time on 21 slams chasing Graf's record, she mentally overcame that slamless barrier and phsyically outlasted the goat in 3 sets at the beginning of the year when players are at their freshest - all the more impressive as Serena had won 4 of the previous 5 slams and made the Semi in the other which she really should have won.
Garbine at the next slam, French open 2016, tactically she outplayed Serena with a clear game pan to push her back on the court as far as possible to reduce the impact of her power, she bullied her really, in her maiden win as well, pretty impressive especially considering how motivated Serena was after losing Australia, not winning enough FO's in the past, chasing the record and the fact she had never lost two grand slam finals in a row at that point.
Osaka US Open 2018, need I say more, how she othercame all of the theatrics and hysteria going on down the other end of the court along with the rude crowd, was beyond me, and at the age of 20, her first slam, a big shame it was ruined by to overcome that sort of adversity is seriously impressive, and served it out with an ace! showed huge mental strength that will never be forgotten.
Azarenka Australia 2013, beat Li Na in the final, defending her crown in a tough 3 setter against not just a player who lost the 2011 final and desperate to win, but she also played against the crowd who were as much Pro Li Na as they were Anti Vika after the trick she pulled against Sloane Stephens in the Semi, only RedFoo in that stadium was supporting her, RedFoo and his silly hair
Hard to put these in order but still.