Stephens makes WTA Finals last 4

SLOANE Stephens has reached the semi-finals of the WTA Finals after knocking out German top seed Angelique Kerber. The American has won all three of her matches in Singapore and saw off world number two Kerber 6-3 6-3 to set up a last-four match with Karolina Pliskova. Japan's US Open champion Naomi Osaka retired from her match against Kiki Bertens with a thigh injury after the Dutchwoman took the first set 6-3. Bertens will face Ukraine's Elina Svitolina in today’s other semi. "I knew it was going to be a battle against one of the toughest players on the tour," said Stephens, 25, who topped her group with the win and recorded her fifth straight victory over the reigning Wimbledon champion. "So I just came out and played as hard as I could and am really pleased with the win." The four lowest-ranked players have progressed to the semi-finals in Singapore, with Kerber and Osaka eliminated along with Caroline Wozniacki and Petra Kvitova from the other group.