Hakuho gobbled winless Yoshikaze up like a Venus' flytrap to retain his share of the early lead at the New Year Grand Sumo Tournament on Thursday.
Hakuho was all business in the day's finale, the Mongolian grand yokozuna yanking down Yoshikaze by the back of the neck and squashing second-ranked maegashira to the dirt after he had tried to counter with a thigh grab.
Hakuho is tied at 5-0 with former sekiwake Wakanosato and 16th-ranked maegashira Tochinonada. Harumafuji dropped out of the pack after a surprise defeat.
Harumafuji's unbeaten start came to an end when he was outmuscled by komusubi Tochiozan (2-3) in the day's main upset at Ryogoku Kokugikan.
Harumafuji pulled out of the Kyushu meet in November with a right ankle injury and must post at least eight wins here to preserve his ozeki status.
Kotooshu never looked in any danger of following suit and biting the dust in the next bout, the burly Bulgarian getting inside Tamawashi (2-3) and spinning the third-ranked maegashira around and down to the sandy surface.