WATCH the WTA Tour LIVE in Australia on beIN SPORTS | Sign up here

The 26 year-old had match point against eventual winner Iga Swiatek in the second round at Roland-Garros but failed to capitalise. However, that defeat was put to the back of her mind, winning 6-2 6-4 in the Netherlands. 

Mertens matched Osaka in the opening exchanges, but the Japanese would rally to take control and win the next three games to secure an early advantage. 

She showed signs of frustration in the second set as the Belgian threatened to take the encounter to a deciding set, but Osaka remained composed to see out the victory. 

Osaka will face Suzan Lamens in the next round. 

Osaka's victory saw her win 28 of her 31 first-serve points, accumulating to a 90 per cent success rate. 

The Japanese claimed her fifth victory over Mertens since their first meeting in Wuhan in 2019, but her triumph was the first encounter between the pair on a grass court.