Serena Williams retains WTA Finals title . Beats Simona Halep 6 - 1 6 - 1 in semifinal match in Singapore . Halep thrashed Williams in round robin match earlier in week . Fourth-ranked Halep began where she left off to take an early 2-1 lead with a break of service , but this was a very different Williams on the other side of the net . Fifth place in season - ending championships for Serena Williams .
Serena Williams retains WTA Finals title . Beats Simona Halep 6 - 1 6 - 1 in semifinal match in Singapore . Halep thrashed Williams in round robin match earlier in week . Fifth place in season - ending championships for Serena Williams .