ASHLEIGH Barty has rallied from a set down to edge past Estonian Anett Kontaveit and book her place in the quarter-finals of the Cincinnati Open.

The top-seeded Australian clinched a battling victory with a deep forehand winner and raised her right fist in triumph after fighting off match point and outlasting Kontaveit in two hours and 10 minutes.

In the process, Barty struck 31 winners and nine aces, breaking Kontaveit six times French Open champion Barty, currently ranked second, can reclaim the world top spot by reaching the tournament final in the US Open warm-up event in Ohio.

"It was a little bit scrappy at times today but proud of the way we were able to fight and hang in there right until the end," said the reigning Roland Garros champion.

"Ultimately that was the most important part about today was to try to hang in there as best that I can, fight right until the end and try and make a match of it.

"Towards the end, I started to find a little bit more rhythm but certainly struggled early on. It was more about the fight today than the tennis."

Into the last eight in Cincinnati for the first time, Barty - who fought past Maria Sharapova in her opener - will play Greece's Maria Sakkari after she dispatched Aryna Sabalenka 6-7 (7-4) 6-4 6-4 to advance.

Venus Williams also rallied from a set down to prevail a 2-6 6-3 6-3 winner against Croatia's Donna Vekic.

Third seed Karolina Pliskova of the Czech Republic is also through, beating Sweden's Rebecca Peterson 7-5 6-4.