Mongolian Hakuho dispatched Kotooshu on Friday to stay tied for the lead with Miyabiyama at the Summer Grand Sumo Tournament in Tokyo.
Ozeki Hakuho got a hold of Kotooshu's belt and flung the Bulgarian ozeki to the dirt surface to maintain his share of the lead at 12-1 in the 15-day event at Ryogoku Kokugikan.
Hakuho, who is making his debut at sumo's second-highest rank in this tourney, is gunning for his first Emperor's Cup and will face Chiyotaikai on Saturday.
It's been a disappointing meet for Kotooshu, who fell to 6-7 and will need to post wins on the final two days just to salvage a winning record.
In other major bouts, sekiwake Miyabiyama stayed in the lead with a hard-fought victory over Mongolian Kyokushuzan.
Miyabiyama fought off a series of arm thrusts from Kyokushuzan and then shoved the fifth-ranked maegashira over the edge with a thrust to the chest.
Kyokushuzan, who landed in the first row of seats, was handed his fourth loss against nine wins.
Estonian Baruto, who is making his debut in the elite makuuchi division, stayed in contention and improved to 11-2 when he got both hands on the belt of Asasekiryu and lifted the No. 2 maegashira over the straw ridge.
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