Caroline Wozniacki won the last 11 points to edge Mihaela Buzarnescu in tight three set tussle, 6-4 3-6 6-3 in two hours and 36 minutes.
Maria Sakkari produced her best performance of the year by a country mile to oust the defending champion and number two seed, Kiki Bertens, 7-6(8) 6-3.
Sakkari came from 1-4 down in the first set and saved four set points in the first set tiebreak.
The number one seed rallied from a set and a double break down, and then a break down in the decider to beat Ajla Tomljanovic, 4-6 6-4 6-4.
Sloane vs. Madison is the pick of Friday’s quarter-finals.