Grand champion Asashoryu won his 10th Emperor's Cup on Friday even before stepping into the ring at the New Year Grand Sumo Tournament.
With two days remaining in the 15-day tourney, Asashoryu clinched the title when fellow Mongolian Hakuho was overpowered by Iwakiyama in an earlier bout at Ryogoku Kokugikan.
Komusubi Hakuho, who dropped to 9-4, was one of just two wrestlers who went into Friday's bouts with a mathematical chance to catch yokozuna Asashoryu. South Korean grappler Kasugao was the other but he lost in an earlier bout to Hokutoriki.
Top maegashira Iwakiyama improved to 7-6 when he completely overpowered Hakuho at the faceoff to send the Mongolian teenager over the straw ridge.
In the day's final bout, Asashoryu put an exclamation point on his title with a hard-fought win over sekiwake Wakanosato.
Wakanosato had Asashoryu on the run but the Mongolian champion turned the tables at the edge before getting both hands on the belt of his opponent and forcing the sekiwake wrestler out to improve to a perfect 13-0. Wakanosato fell to 6-7.
"I just tried to stay focused even though I knew I had already won," said Asashoryu. "It's nice to win the first tournament of the year."
Asashoryu won five of six tournaments last year and looks poised for another impressive run this season. He is the lone yokozuna currently competing in sumo.
Ozeki Kaio went into the New Year tourney hoping for promotion to the sport's highest rank but had a disastrous outing and pulled out on Tuesday with an unimpressive 4-5 record with one default.
In other major bouts, Chiyotaikai edged toward the winning record he needs to maintain his ozeki status when he used his trademark arm thrusts to send Russian Roho backpedaling over the straw ridge.
Chiyotaikai improved to 7-6 while No. 5 maegashira Roho dropped to 5-8.
Sekiwake Tochiazuma improved his chances of returning to ozeki status when he used a series of powerful arm thrusts to send No. 4 maegashira Kakizoe over the straw ridge.