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 3-5 down and breaking back when Zheng served for the set at 6-5.
The Czech was down 3-6 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 on court after the match.
Kvitova will meet either her fellow countrywoman Barbora Krejcikova or world No.8 Daria Kasatkina, of Russia, in the last eight.
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.
She is coming off back-to-back victories in the United Cup where she beat Germany's Laura Siegemund and world No.3 Jessica Pegula, of the USA, in straight sets.
American Danielle Collins, who made the final of the Australian Open last year, also progressed to the quarter-finals with a 6-3 7-6 (7-2) win over Swiss qualifier Jil Teichmann.
