American qualifier Lauren Davis claimed a shock 6-1 6-3 victory over second seed Sorana Cirstea in the second round of the Moorilla Hobart International.
Davis needed a little under 90 minutes to see of the world No 27, who was broken a total of four times and barely won half of the points on her serve.
Compatriot Sloane Stephens awaits Davis in the quarter-finals after the eighth seed wasted no time in seeing off Simona Halep 6-4 6-0.
With Hsieh Su-wei being defeated by Peng Shuai on Monday, the top two seeds at the Australian tournament have now been eliminated.
Third seed Klara Zakopalova is still in the mix as she claimed a straightforward 6-4 6-3 victory over Timea Babos in the first round.
But No 4 seed Yaroslava Shvedova has also been eliminated as Elena Vesnina came from a set down to claim a 4-6 6-2 6-1 win over the Kazakh in round two.
Mona Barthel became the fourth player to book her spot in the last eight on Tuesday as the ninth seed defeated Chanelle Scheepers 7-6 (7-3) 7-5.