Ovtcharov, the top seed, looked to be on his way to a shock defeat before he recovered to claim an 8-11, 8-11, 11-6, 11-2, 11-8, 11-9 victory to seal his place in the quarter-finals at the Arena Asarel.

The four-time Olympic medallist will take on Mizuki Oikawa in the next round after the Japanese player accounted for team-mate Yukiya Uda with a 11-1, 11-6, 11-6, 11-7 win.

Third seed Quadri Aruna of Nigeria also struggled to get going in his round of 16 match against Yuto Kizukuri of Japan as he lost the first two games.

Aruna followed pre-tournament Ovtcharov in launching a spirited comeback as he eventually secured a 9-11, 7-11, 12-10, 4-11, 11-9, 13-11, 11-9 triumph.

Japan are guaranteed to claim the women's singles crown as all of the last 16 players left in the tournament before today hail from the Asian country.

Top seed Kasumi Ishikawa, a double Olympic medallist in team events, breezed into the quarter-finals as she comfortably beat Mizuki Morizono in straight games.

Ishikawa was in ominous form and sent out a warning to the rest of the field with an 11-5, 11-9, 11-8, 11-6 success.

She will meet Asuka Sasao, who stunned seventh seed Georgina Pota of Hungary yesterday, after she overcame 12th seed Maki Shiomi 11-7, 9-11, 7-11, 11-9, 11-8, 12-10.

Hitomi Sato, the third seed, also progressed to the last eight as she dropped two games on her way to a 11-7, 11-13, 11-7, 11-8, 5-11, 11-9 victory over Yui Hamamoto.

Miyu Kato awaits for Sato in the quarter-finals after she ousted Misaki Morizono 9-11, 11-4, 11-6, 11-6, 12-0.

The tournament continues tomorrow.