Ashleigh Barty has officially secured the year-end world No.1 tennis ranking.

After a stellar season highlighted by her breakthrough French Open triumph in June, Barty arrived at the WTA Finals with a huge rankings lead over her rivals.

Victory over Belinda Bencic in her opening round-robin encounter left the top seed only needing to step on court for her second match on Tuesday night.

Barty has done so, meaning the 23-year-old becomes the first Australian since Lleyton Hewitt in 2002 to finish a season atop the rankings.

No Australian woman has ever managed the feat.

Barty is playing Kiki Bertens after the Dutch alternate replaced injured world No.3 Naomi Osaka.

Osaka also won her opening match on Sunday, against Petra Kvitova in a repeat of her 2019 Australian Open final success over the Czech, before withdrawing from the season finale with a shoulder complaint.

A win over Bertens would also thrust Barty into the semi-finals in Shenzhen.