Daria Kasatkina produced a marvellous performance to beat Australian Open champion and new world number one Caroline Wozniacki in the St Petersburg Ladies Trophy.
Wozniacki's has been the toast of women's tennis after defeating Simona Halep to win her first grand slam title in Melbourne, but was brought back down to earth by 20-year-old Kasatkina.
The home hope came from a break down to take the first set on a tie-break and saw off a Wozniacki recovery from 3-0 down in the second to complete a 7-6 (7-2) 6-3 victory.
Benefiting from 35 unforced Wozniacki errors, Kasatkina faced a break point as she served for the match, but saved that and wrapped things up in style with a backhand drop shot followed by an impressive pickup on the forehand.
Next up for Kasatkina, who also reached the semi-finals in 2016, is defending champion Kristina Mladenovic. The Australian Open doubles champion, who came into the tournament on the back of a 15-match losing streak in singles, has now won successive contests in straight sets after defeating Katerina Siniakova 6-4 6-3.
Petra Kvitova is also into the last four after hammering second seed Jelena Ostapenko 6-0 6-2.
Kvitova looked as if she was still finding her best form following her return from a hand injury sustained in a knife attack in December 2016 as she was dumped out in the first round in Melbourne.
But she knocked out seventh seed Elena Vesnina in the first round in Russia and, after dispensing with Irina-Camelia Begu in the second round, thrashed second seed and French Open champion Ostapenko to book a semi-final with fifth seed Julia Goerges, who beat Elena Rybakina 6-3 6-3.
At the Taiwan Open, Sabine Lisicki is a win away from her first WTA final since September 2014 after coming from behind to defeat Monica Niculescu.
The 2013 Wimbledon finalist made her return from shoulder surgery in June, but a knee injury delayed her start to the 2018 season.
However, she demonstrated plenty of resolve in fighting back to beat Niculescu 4-6 6-4 6-4. She will now face Kateryna Kozlova in the last four after the Ukrainian beat fifth seed Yulia Putintseva 7-5 6-3.
Fourth seed Timea Babos, who won the Melbourne doubles with Mladenovic, overcame Magda Linette 6-1 6-3.
Eugenie Bouchard can console herself with a trip to the Super Bowl with famous Twitter date John Goehrke after her hopes ended with a 6-4 6-0 loss to Yafan Wang.