Azarenka, Kvitova score

Belarusian Victoria Azarenka made a winning return to Stuttgart with a 7-5, 6-4 victory over Russia's Vera Zvonareva in what was an engrossing battle in the first round of the Porsche Tennis Grand Prix on Wednesday.

Azarenka, a former world number one, was pushed in the opening set, especially by Zvonareva's first serve, but fought back to break her four times in the match. The last time the pair met was in 2011 when they were both ranked in the top 10.

"We're both in completely different stages of our careers, we're both moms," Azarenka said.

"I think I'm playing better than I used to before, I believe I'm much more of a complete player than I used to be. I'm in the process of building my game up again."

The 29-year-old, a two-time Australian Open champion, also had to overcome jet lag after competing in the Fed Cup semifinal in Australia at the weekend.

Azarenka will take on fourth seed and defending champion Karolina Pliskova next for a spot in the quarterfinals.

World number three Petra Kvitova, who received a bye to the second round, cruised through to the quarterfinal with a 6-1, 6-4 win over Belgian qualifier Greet Minnen.

Minnen was no match for Kvitova in the first set but found her groove in the second to test the Australian Open runner-up. However, it was too little too late for the 21-year-old as Kvitova wrapped up the match in 73 minutes.

Earlier, Switzerland's Belinda Bencic started the tournament strongly with a 6-2, 6-4 victory over qualifier Mandy Minella.

Bencic struck 24 winners with her aggressive returns dominating the Luxembourger. The result pits Bencic against sixth seed Kiki Bertens.

Last year's semifinalist Anett Kontaveit of Estonia breezed past France's Caroline Garcia with a 6-4, 6-3 win while Donna Vekic beat Giulia Gatto-Monticone 6-1 7-5 to advance.

Julia Goerges' first match was cut short by injury with the German forced to retire when she was trailing 4-0 in the final set to Anastasia Pavlyuchenkova. Goerges had taken the first set 6-4 before the Russian took the second 6-2.