Top seed Ashleigh Barty rallied from a set down to edge past Estonian Anett Kontaveit and book her place in the quarter-finals of the Cincinnati Open.
The 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.
Barty struck 31 winners and nine aces, breaking Kontaveit six times, but also made a worrying 49 unforced errors.
French Open champion Barty, currently world No.2, can reclaim the world top spot by reaching the tournament final in the US Open warm-up event in Ohio.
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.
"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."
World No.1 Naomi Osaka survived a tough test against Hsieh Su-Wei before winning 7-6 (7-3) 5-7 6-2.
Osaka, who lost to Hsieh at the Miami Open in March, admitted a day earlier that the Taiwanese challenger was an unpredictable opponent for her.
But she was ready this time around, firing 15 aces and breaking Hsieh five times.
"I thought I did pretty well," Osaka told reporters afterwards. "I feel like I knew going into the match that she was going to play really well. Like, we have such long matches every time we play, so I wasn't expecting anything different this time around."
Venus Williams 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.