Kasatkina arrived in Zhuhai on a high after securing the second title of her career at the Kremlin Cup in her homeland and hit the ground running with a 6-1 2-6 7-5 Azalea Group victory on Wednesday (AEDT).

The world number 10 made hard work of seeing off Wang after dominating the first set, serving out the win after nine consecutive breaks in the decider.

Russian Kasatkina failed to hold four times in the second set and as many in the third, racking up nine double faults before finally ending the 11th seed's resistance.

Mertens had no such trouble, taking just 66 minutes to move to the top of the Rose Group with a 6-3 6-1 defeat of Anett Kontaveit.

The fourth seed, winner of three WTA titles this season, has struggled on the Asian swing, but broke Kontaveit six times in a promising start.

Sabalenka, the youngest player in the history of the season-ending tournament at the age of 20, also needed just the two sets to beat Ashleigh Barty in the Orchid Group.

Third seed Sabalenka won 78 per cent of points on her first serve and was broken just the once, winning the opening match of the tournament 6-4 6-4.