TOKYO — Grand champion Asashoryu of Mongolia was upset on the opening day of the Summer Grand Sumo Tournament today, falling to Kisenosato in the day's final bout.

Asashoryu, who is gunning for his 23rd Emperor's Cup, was pushed back by the komusubi wrestler at the faceoff and was knocked down as he struggled to find his footing on the straw ridge.

Asashoryu's loss was met by joyous celebrations at Ryogoku Kokugikan where seat cushions were flung from the upper seats as the bad boy Mongolian made his way off the raised ring.

Elsewhere, Asashoryu's main rival Hakuho got off to a winning start.

Hakuho, who has made a habit of losing on the opening day, swatted komusubi Asasekiryu down shortly after the faceoff for a comfortable win.

Mongolian Hakuho will be looking to avenge a final-day loss to Asashoryu at the Spring Grand Sumo Tournament in March.

In the other major bouts, ozeki Kaio overcame a determined effort by Baruto to pick up an opening-day victory.

Kaio shoved the top maegashira from Estonia back to the edge twice before finally sending his opponent over with one final push.

Ozeki Chiyotaikai used his trademark arm thrusts to overpower No. 2 maegashira Kyokutenho of Mongolia.

Chiyotaikai is nursing an injured right elbow but looked in good form in Sunday's win.

Bulgarian Kotooshu, who needs a winning record in this tourney to maintain his ozeki status, got both hands on the belt of No. 2 maegashira Wakanoho and lifted the Russian wrestler over the straw ridge for an easy win.

Kotomitsuki made it a clean sweep for ozeki on opening day when he used an arm throw at the center of the ring to send Kokkai toppling to the dirt surface.

Georgian Kokkai enters the tournament as a top maegashira.

Mongolian sekiwake Ama forced out No. 3 maegashira Miyabiyama to open with a win.