Bulgaria's No.1 female tennis player Tsvetana Pironkova won her match against Madison Keys (USA) in the second round of the women's singles competition at the Sydney Apia International tournament.

The score was 4:6, 4:1 when the American retired after suffering an injury to her right shoulder, electronic daily Dnevnik reports.

In the first match between the two, which was played at the Indian Wells tournament last season, Keys defeated Pironkova with 6:2, 6:1.

Both tennis players started the match concentrated with the first opportunity for a break occurring in the tenth game when Pironkova was serving.

Keys, who was in the lead with 5:4, made a break and closed the first set with 6:4.

The second set started well for Pironkova, who achieved two breaks and was in the lead with 3:0.

Keys returned a break for 3:1, but after that she retired due to an injury to her shoulder.

Pironkova, who is the reigning champion in Sydney, recorded her 13 successive victory in the tournament and continues the successful defence of her title.

In the third round the Bulgarian will face Barbora Zahlavova-Strycova from the Czech Republic, who defeated the Australian Samantha Stosur.