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The contest had been paused with the four-time grand slam champion leading 5-4 in the first set, due to persistent rain in Germany.

Frech had remarkably rallied to get the set back on serve after going 5-0 down, but the long delay worked in Osaka's favour as she rediscovered her groove.

Osaka broke at the first opportunity after the restart, taking the opening set, and that was the first of six consecutive games that went her way as she cruised through the second.

Even Frech's lone hold was a difficult one, and Osaka served out the contest to love to tee up a meeting with Elise Mertens or Alexandra Eala – who reached the semi-finals of the Berlin Open last week following top-10 wins over Elena Rybakina and Elina Svitolina. 

Meanwhile, Iva Jovic was forced to withdraw from her scheduled round-one clash with Wang Xinyu due to an ankle injury, just one week out from the start of Wimbledon.