World number one Ash Barty battled back from a set down to beat Czech Republic's seventh seed Petra Kvitova 4-6 6-4 6-3 to advance to the semi-finals of the China Open in Beijing on Friday.
French Open champion Barty, who had been beaten twice by Kvitova in Australia earlier this year, fired nine aces and converted three of six break points to win the encounter.
"That was one of the highest quality matches I played all year," Barty told reporters. "Petra always has a way of bringing out the best in me, she really does.
"From both of us, I think the level was incredible. Regardless of winning or losing, I think I'd be sitting here with the exact same perspective, kind of the same feeling of the match afterwards."
Although Kvitova, a two-times Wimbledon champion, fired 36 winners to Barty's 31, her unforced error count of 28 proved to be her downfall.
The Czech saved three match points when Barty served for the match at 5-3 in the decider but the Australian fought back to deuce and then fired a crosscourt forehand winner to move into the tournament's semis for the first time in her career.
Barty will face eighth seed Kiki Bertens, who upset third seed Elina Svitolina 7-6(6) 6-2.
In another battle of Grand Slam champions, Japan's Naomi Osaka beat U.S. Open holder Bianca Andreescu 5-7 6-3 6-4 in a thrilling encounter, ending the Canadian's 17-match winning streak to book her place in the semi-finals.
"I forgot how it felt and honestly it sucks, I didn't miss it," Andreescu said after her first loss since the Miami Open in March and her first loss against a top 10 opponent. "Hopefully that was fun.
"I think we're going to have many matches like this. Our game styles are pretty different, but they level up pretty equally."
Osaka fired 10 aces, 31 winners and won 78% of her first service points in a see-saw encounter that had a total of 11 breaks of serve. She will play defending champion Caroline Wozniacki, who beat Russia's Daria Kasatkina 6-3 7-6(5).
Osaka became the fifth player to qualify for the season-ending WTA Finals in Shenzhen after Barty, Karolina Pliskova, Wimbledon champion Simona Halep and Andreescu.