Grand champion Asashoryu was handed his second straight defeat Thursday when he was shoved out by Iwakiyama on the fifth day of the Autumn Grand Sumo Tournament.
Mongolian Asashoryu, who was upset by Tochinonada on Wednesday, was shoved back at the faceoff in the day's final bout at Tokyo's Ryogoku Kokugikan and was unable to regain his footing before being forced out by the determined No. 2 maegashira.
Iwakiyama improved to 4-1 while Asashoryu fell to 3-2 and is now two wins off the lead.
Asashoryu is aiming for his fifth straight Emperor's Cup and vowed before the start of the Autumn tournament that he would win all six tournaments this year.
In other major bouts, ozeki Kaio, who lost to Kotomitsuki on Wednesday, used his weight advantage to bulldoze winless No. 2 maegashira Tamanoshima out of the ring in a matter of seconds.
Kaio improved to 4-1 and is one of five wrestlers who stand one win off the pace.
Earlier, No. 5 maegashira Dejima muscled out seventh-ranked Takekaze to maintain a share of the lead at 5-0, along with Mongolian Kyokushuzan and No. 16 maegashira Takanotsuru.
Kyokushuzan tripped up fourteenth-ranked maegashira Kotooshu while Takanotsuru upended No. 15 Toyonoshima.
Ozeki Chiyotaikai rebounded from Wednesday's loss to Iwakiyama when he took advantage of a poor faceoff by Mongolian Kyokutenho and swatted the komusubi down to improve to 4-1. Kyokutenho fell to 3-2.
Rising star Hakuho, a No. 3 maegashira, humbled ozeki Musoyama with a textbook arm throw that allowed the 19-year-old Mongolian to improve to 3-2.
Musoyama, who was never able to gain control of his opponent's belt, fell to 1-4 and is just one of several higher-ranked wrestlers struggling in the Autumn meet.