Australian squash No.1 Kasey Brown has surprised Hong Kong's sixth seed Annie Au in straight games to reach the quarter-finals of the US Open in Philadelphia.

Brown defeated Au 12-10 11-8 11-9 to become the only Australian to win on Monday.

The 27-year-old world takes on second-seeded Egyptian Raneem El Weleily for a place in the semi-finals.

"It was kind of a blessing in disguise not being the seeded player for once," said Brown, who reached the final last year.

"She beat me in Malaysia, but Rod (Martin) and I came up with a new game plan against her, attacking more, and it worked.

"But all three games were close."

Fellow Australians Rachael Grinham, Donna Urquhart and Cameron Pilley all bowed out.

Third seed Jenny Duncalf beat Grinham 11-5 11-8 11-4 while fifth-ranked Madeline Perry defeated Urquhart 11-5 11-4 7-11 11-2.

In the men's draw, eighth seed Mohamed El Shorbagy beat Pilley 10-12 11-8 12-10 10-12 11-4 in a five-game epic.