Kanepi, now ranked 31st in the world, won the opening set on a tie-break, 7:6 (4), and was 3:0 up in the second set when Osaka forfeited.

Kanepi said: "It's a pity to see the game ending like that for her. I've had many matches where my opponent has taken a medical break, and it doesn't bother me much."

After Kanepi broke Osaka's serve in the third game of the first set, Osaka summonsed a doctor on court, complaining of back pain. Carrying on, she was nonetheless able to break the Estonian's serve twice and take things to a tie-break situation, which Kanepi wrapped up quickly after breaking Osaka's service twice.

The first set lasted just under an hour.

Fourteen minutes into the second set, Kanepi was 3:0 up, at which point Osaka forfeited.

The Estonian, 37, from Haapsalu, faces another former world number one, Garbine Muguruza (Spain), seeded eighth in the tournament.

The Canadian Open, played at the IGA Stadium (Montreal) and Sobeys Stadium (Toronto) is one of several North American warm-up competitions taking place ahead of the U.S. Open later this month.

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