Kiki Bertens beat world number one Ashleigh Barty at the WTA Finals just hours after being added to the tournament as a replacement.

The Dutch world number 10 took the place of Naomi Osaka, who withdrew on Tuesday with a shoulder injury.

Bertens was trailing by a set and a break but Australian Barty collapsed as Bertens won 3-6 6-3 6-4 in Shenzhen.

Barty lost seven games in a row from 3-3 in the second set after a series of errors and could not recover.

Bertens had herself started poorly, only holding serve once in four attempts in the first set.

She then twice trailed by a break in the second set - at 2-1 and 3-2 - before Barty's level dropped.

French Open champion Barty fought back from 4-0 to 5-4 in the third set but Bertens closed out the match on serve at the first opportunity.

More to follow.