World No. 1 Victoria Azarenka moved into the Stuttgart indoor tournament quarter-finals on Thursday as sixth-seed Caroline Wozniacki was upset by Angelique Kerber.
Azarenka will face in-form Mona Barthel of Germany for a place in the last four after Germany’s Andrea Petkovic retired with an ankle injury while trailing the Belarussian top seed 6-2, 4-4.
Azarenka grabbed a break in the opening game, but missed an easy volley to hand it back in the fourth game to Petkovic, who had only this week returned to the Tour after almost four months out with a back injury.
She then proceeded to break the German again to take the first set 6-2.
The second set initially followed a similar pattern, with Azarenka breaking in the first game courtesy of a stunning double-handed backhand down the line before being broken straight back.
World No. 12 Petkovic looked set to give her opponent a tougher time, but badly twisted her ankle as she tried to hit a forehand at 4-4 with the indoor crowd instantly falling deadly quiet.
“It’s such a tough situation and the ankle right away blew up,” Azarenka said in a courtside interview.
“I hope she recovers soon because she is a great player. Andrea is one of the players who is tough mentally, she is a great fighter,” she said.
German Mona Barthel kept up her spectacular form this year with a 6-3, 6-1 demolition of world No. 7 Marion Bartoli to book her spot in the last eight and notch her first career victory over a top-10 player.
“It was one of the best matches of my life,” said Barthel, who won her maiden WTA title in Hobart in January.
“I was immediately able to put her serve under pressure. It’s great to have won my first match against a top 10 player. It’s something special,” she said.
World No. 5 Sam Stosur avenged last year’s semi-final defeat by Julia Goerges, beating the German defending champion 6-2, 2-6, 6-3 to set up a quarter-final against world No. 2 Maria Sharapova.
German Kerber also caused a major upset, dismantling former world No. 1 Wozniacki 6-1, 6-2 to set up a mouth-watering clash with Wimbledon champion Petra Kvitova.
The Czech advanced with a comfortable straight-sets victory over Italy’s Francesca Schiavone, while China’s Li Na beat Akgul Amanmuradova of Uzbekistan 6-4, 6-4.
GRAND PRIX SAR
AP, FEZ, MOROCCO
Two-time runner-up Simona Halep knocked out top-seeded Anabel Medina Garrigues of Spain 6-2, 6-1 to reach the semi-finals of the Grand Prix SAR on Thursday.
The fifth-seeded Halep, who lost the past two finals, did not face a single break point and broke Medina Garrigues’s serve five times.
Halep is the only seeded player remaining in the tournament and the Romanian next faces qualifier Kiki Bertens of the Netherlands, who advanced to the last four by beating Spain’s Garbine Muguruza Blanco 6-1, 6-4.
In another upset, Mathilde Johansson of France beat third-seeded Petra Cetkovska of the Czech Republic 6-3, 6-4 to set up a semi-final against Spain’s Laura Pous-Tio.