St Petersburg - Australian Open finalist Petra Kvitova continued her strong run of form with a straight-sets win over former world number one Victoria Azarenka to reach the quarter-finals in Saint Petersburg on Wednesday.
Two-time Wimbledon champion Kvitova, who rose to world number two after her Melbourne final loss to Naomi Osaka last Saturday, prevailed 6-2, 7-6 (7/3).
She led 5-1 in the second set and missed two match points before ending an Azarenka comeback in a tie-break.
"I really wanted to finish (the match) earlier, but unfortunately I had to fight back in the second set and then I did quite well in the tie-break," said Kvitova.
Two-time Australian Open winner Azarenka, who has tumbled down the rankings since the birth of her son Leo and an ensuing custody battle, has still not reached a WTA final since winning the 2016 Miami Open.
In the quarter-finals, Kvitova will face eighth-seeded Donna Vekic of Croatia, who cruised past lucky loser Veronika Kudermetova 6-4, 6-3.
Elsewhere, Russian veteran Vera Zvonareva battled back from a set down to beat fifth seed Julia Goerges of Germany 4-6, 6-4, 6-4 as she looks to rediscover the form which took her to the 2010 Wimbledon and US Open finals.
The 34-year-old, now ranked 97th, will next face third seed Daria Kasatkina, who is yet to play a match in the tournament having enjoyed an opening-round bye before advancing after Maria Sharapova pulled out with a shoulder injury.
Results from the Saint Petersburg WTA tournament on Wednesday (x denotes seeding):
Petra Kvitova (CZE x1) bt Victoria Azarenka (BLR) 6-2, 7-6 (7/3)
Donna Vekic (CRO x8) bt Veronika Kudermetova (RUS) 6-4, 6-3
Daria Kasatkina (RUS x3) bt Maria Sharapova (RUS) -- walkover
Vera Zvonareva (RUS) bt Julia Goerges (GER x5) 4-6, 6-4, 6-4
Ekaterina Alexandrova (RUS) bt Katie Boulter (GBR) 7-5, 4-6, 6-1