Ozeki Chiyotaikai beat Musashimaru at the face-off and the yokozuna leader never had a chance, getting bulldozed out of the ring to his first loss at the Summer Sumo Grand Tournament on Friday.
Musashimaru, who was expected to secure his 11th Emperor's Cup with a win on the 13th day at Tokyo's Ryogoku Kokugikan, was caught lead-footed in his crouch, handing the advantage to the ozeki who quickly dispensed with the yokozuna in a flurry of slaps to the chest.
The loss left Musashimaru with a 12-1 record with two days remaining in the 15-day meet. A win on Saturday or Sunday will still wrap the championship up for the Musashigawa stable grand champion.
Chiyotaikai and 14th-ranked maegashira Hokutoriki, both at 10-3, are the nearest pursuers for the coveted hardware and could still claim a spot in a playoff with the Samoa-born yokozuna if Musashimaru would happen to lose his last two bouts of the tourney.
The ozeki and rank-and-filer, however, must also win their final two matches to stay in contention.
At ozeki, Musoyama (9-4) cringed in pain from an apparent strained shoulder when fourth-rank maegashira Kyokutenho (6-7) employed an arm-maneuver to fling the Musashigawa ozeki from the ring.
Kaio (9-4) dealt ozeki rival Tochiazuma (9-4) a devastating blow when he circled around from the right for a well-timed arm-lock throw.