Kvitova, Collins into Adelaide quarters

Two-time Wimbledon winner Petra Kvitova is through to the quarter-finals of the Adelaide International 2 after Qinwen Zheng pulled the pin with a leg problem during their round-two match.

The Chinese world No.30 retired on Wednesday after dropping the first set 6-7 (6-8) and squandering three set points in the tiebreaker.

She called for the trainer after the set and opted not to continue.

Kvitova earlier called on her fighting spirit, coming back from 5-3 down and breaking back when Zheng served for the set at 6-5.

The Czech was down 6-3 in the tiebreak before winning the final five points of the match.

"It's not nice to end the match as we (did). I wish her all the best for the (Australian Open), which is soon," Kvitova said.

Kvitova will meet world No.8 Daria Kasatkina in the last eight after the Russian beat Barbora Krejcikova 6-2 7-5.

Kvitova, who has been ranked as high as No.2 in the world and currently sits at No.16, had an impressive win over reigning Wimbledon champion Elena Rybakina in the first round.

The 2021 Australian Open finalist is coming off back-to-back victories in the United Cup where she beat Germany's Laura Siegemund and American world No.3 Jessica Pegula in straight sets.

American Danielle Collins, who lost last year's Australian Open to Ash Barty, also progressed to the quarter-finals with a 6-3 7-6 (7-2) win over Swiss qualifier Jil Teichmann.

World No.13 and 2020 Olympic gold medallist Belinda Bencic beat qualifier Anna Kalinskaya, while Brazil's Beatriz Haddad Maia toppled Amanda Anisimova 6-4 7-5.

In the late match, France's Caroline Garcia, the top remaining seed, earned a hard-fought 6-3 3-6 7-5 victory over Katerina Siniakova to earn a tie with Bencic.

Garcia battled a fierce rearguard action from the Czech to prevail in just over two hours as the contest closer just before midnight.

"She (Siniakova) played some unbelievable tennis which caused me a lot of issues," Garcia said in her on-court interview.

"In the last couple of games, I was able to be more solid and bring back more returns, same as the first set. I was a little bit aggressive on few shots and tried to be closer to my baseline."