An early goal from Shingo Akamine put Sendai ahead before Brazilian forward Wilson doubled the lead on the stroke of halftime.
Omiya, who had last suffered defeat in the league on Aug. 25 last season, also to Sendai, pulled a goal back through Zlatan Ljubijankic after 65 minutes but were unable to find an equaliser to extend their amazing streak.
Omiya manager Zdenko Verdenik said winning the league, not setting records, had been the priority for his team.
"The unbeaten record was never something that we gave a lot of thought to. We are not playing soccer to set records," Zdenko Verdenik was quoted as saying by Japan's Kyodo News.
"Our aim has always been to finish the season as high up the table as we can. That is what is important and we have to keep on trying to rack up the points in each and every match from here on."
Omiya are top of the J.League with 26 points from 11 games, three ahead of Yokohama F Marinos.