The 38-year-old won the ASB Classic in Auckland, New Zealand on Sunday, her first title since winning the Australian Open in 2017 and since she became a mother.

Williams in the process became the first player in the Open era to win titles across four decades. 

Australia's Ashleigh Barty remains top of the rankings but second placed Karolina Pliskova of the Czech Republic has narrowed the gap heading into the Australian Open. Barty is looking to become the first Australian to win the Grand Slam since Christine O'Neil in 1976. 

Japan's Naomi Osaka moves up one place to third while Romania's Simona Halep came down to fourth. Swiss Belinda Bencic moved up to seventh at the expense of Czech Petra Kvitova.