Mongolian yokozuna Hakuho squandered the chance to seize sole possession of the lead with a shock defeat to ozeki Goeido at the Summer Grand Sumo Tournament on Thursday.
Overnight co-leader Kaisei suffered his second loss of the tournament at the hands of fellow maegashira Aoiyama, but Hakuho failed to take advantage in the day's penultimate bout at Ryogoku Kokugikan, dropping to 10-2.
Goeido, who entered the bout having dropped five of his previous 11 matches, came on strong at the charge and after being pushed back, the ozeki went in again to topple the yokozuna with a headlock throw.
It was a close call as both wrestlers crashed to the dirt and Hakuho looked miffed at the decision. However, television replays showed his elbow had touched the dirt a fraction before Goeido hit the floor.
Ozeki Kisenosato, who was also upset, is in a six-way tie for second at 9-3.
It was a bad day all around for sumo's top rank as Harumafuji (8-4) was blasted into the ringside cushions by sekiwake Myogiryu (5-7).
In one of the day's most entertaining bouts, Bulgarian Aoiyama (8-4) prevailed against Kaisei after the advantage had swung back and forth between the two, the No. 6 taking down the Brazilian No. 11 with a beltless arm throw at the edge of the ring.
In other matches, Kisenosato looked to be in trouble early on, sekiwake Terunofuji (9-3) gathering momentum and flooring the ozeki with a shitatenage underarm throw.
Kotoshogiku, however, was never in danger in a bout he could ill afford to lose against Takayasu (9-3), the ozeki charging out his eighth-ranked opponent in a matter of seconds to post a sixth win.