WASHINGTON, Aug. 15 (Xinhua) -- Top-seeded Ashleigh Barty reached the quarterfinals after beating Anett Kontaveit 4-6, 7-5, 7-5 on Thursday.

"The best thing is when my back was against the wall, the tennis was there," Barty said. "It may not have been there the whole match, but we were able to find it when we needed it."

Barty, the French Open champion and currently ranked No. 2, can move up to the top spot by reaching the final.

Venus Williams also secured her place in the quarterfinal. With the crowd cheering for her, Williams recovered from a rough first set to beat Donna Vekic 2-6, 6-4, 6-3, her best stretch of tennis in since she won three straight matches in March at Miami.

After a first-round loss in Toronto last week, her ranking slipped to No. 65, her lowest in seven years.

Serena Williams withdrew from the tournament because of back spasms. She calmly watched her sister advance.

Nick Kyrgios was fined 113,000 US dollars by ATP for expletive-filled outbursts that included smashing rackets, insulting a chair umpire and refusing to get ready to return serve during a second-round match the previous night.