Serena Williams became the first player to reach the semi-finals of the end of season WTA Championships with another dominant display in Istanbul.
The world No 1 beat fifth seed Petra Kvitova 6-2, 6-3 to guarantee top spot in the red group. Earlier,
Li Na battled past Jelena Jankovic for her second win of the tournament, meaning the Chinese player will qualify for the semi-finals if she wins a set from her final white group match against Victoria Azarenka.
On the men's tour, top-seeded David Ferrer made the Valencia Open quarter-finals by easing past Julien Benneteau of France 6-2, 6-1.