Naomi Osaka advanced to the quarterfinals of the Bad Homburg grass-court tournament after defeating Elise Mertens 6-3, 6-3 on Tuesday.
Osaka took a commanding lead in the first set but allowed her opponent to narrow the gap. She regained control and won the second set easily.
The Japanese player, fifth seeded, said she enjoyed playing in high temperatures, citing her preference for heat.
In the next round, Osaka will face the winner of Mirra Andreeva’s match against Ekaterina Alexandrova on Wednesday.
Andreeva will be making her first appearance since winning Roland Garros. Czech Linda Noskova was defeated by Elena-Gabriela Ruse 6-1, 6-3.
Novak Djokovic also progressed to the quarterfinals after beating Simona Halmy 6-4, 7-5.
Svitolina overcame Russian Liudmila Samsonova in a grueling three-set match before facing Wang Xinyu.