Li Na of China swept past injured Victoria Azarenka 6-2, 6-1 on Friday to earn a place in the semi-finals of the WTA Championships in Istanbul.
Azarenka hurt her back while serving in the sixth game of the first set and was clearly in pain the rest of the match. The No 2 player took a medical timeout and received treatment during several changeovers. She stayed on court despite poor movement and wincing in pain.
Azarenka did win one game with some ferocious serving, but mostly stayed in the middle of the baseline and tried to hit quick winners.
Li won the group 3-0, while Azarenka finished 1-2.
Jelena Jankovic will play defending champion Serena Williams in the semi-finals. Williams swept her group on Thursday.
The fourth-seeded Li will play either Petra Kvitova or Angelique Kerber.