Kawasaki Frontale blew the chance to go top of the J-League on Saturday as they lost 2-0 at Yokohama F-Marinos where a small pocket of home fans racially taunted Brazilian player Renato.
Banana-waving fans were caught on video which found its way onto social media in a rare incident of racial abuse in Japanese football.
It remains to be seen whether the J-League will punish Yokohama, although Urawa Reds were ordered to play behind closed doors after fans unfurled a "Japanese Only" banner earlier this year.
J-League leaders Reds escaped with a 4-4 draw after a controversial late penalty from substitute Tadanari Lee to maintain their slender advantage at the top.
Urawa have 41 points from 21 games, one ahead of surprise package Sagan Tosu and two clear of Kashima Antlers, who both won away from home.
Frontale slipped to fourth behind Kashima on goal difference.
Lee tucked away a penalty 10 minutes from time, the third of three contentious spot kicks awarded in a match full of horror defending which will have concerned watching Japan coach Javier Aguirre.
The Mexican, yet to name his squad before his first match in charge of the Blue Samurai at home to Uruguay on September 5, will have been buoyed by two clinically taken goals by FC Tokyo striker Yoshinori Muto.
As Urawa got out of jail after being 3-1 down, Yokohama upset Frontale, an early Rafinha penalty and a neat finish from substitute Shingo Hyodo seeing off the the high-flying visitors.
Kyushu-based Sagan won 3-1 at Omiya Ardija while seven-times champions Kashima overpowered Shimizu S-Pulse by the same score to create a logjam at the top of the first division table.
Champions Sanfrecce Hiroshima were held to a goalless draw at home by Cerezo Osaka on a sombre occasion marked by a minute's silence in memory of more than 40 people killed in landslides in the city in midweek.
Gamba Osaka's 3-3 draw at Ventforet Kofu featured a fifth goal in seven games for former Bayern Munich striker Takashi Usami, a right-foot rocket which could force him into Aguirre's plans.
Bottom club Tokushima Vortis, already being written off as odds-on relegation favourites, stunned Albirex Niigata 2-1 away for their third win of the season to give them a glimmer of hope.
They now have 12 points, four adrift of Omiya who are second from bottom.