Ryota Hayasaka struck early on to hand Sagan their eighth victory of the season as they moved to the summit, while the Red Diamonds dropped into second - a point back - after a goalless stalemate at Vantforet, who had Hideomi Yamamoto sent off in the final minute.
In third, Kashima Antlers suffered a 2-1 defeat at home to mid-table Nagoya Grampus Eight to sit level on points with both Sanfrecce Hiroshima, whose match against Yokohama F Marinos was postponed, and Albirex Niigata.
Yoshizumi Ogawa handed Nagoya the lead before Jose Silva Davi equalised with a penalty just before the break, but Keiji Tamada's second-half winner sealed the points for the visitors.
Albirex claimed a 2-1 home victory over Shimizu S-Pulse with Atomu Tanaka putting them ahead after the break before Yasuhiro Hiraoka pulled one back for the away side late on but Calvin Jong-a-Pin put the ball into his own net to hand the home side victory.
Rodrigues Wilson netted a second-half brace for Sendai with Yoshiaki Ota and Yuki Muto also on target, while Marcos Marquinhos, Pedro Junior and Keijiro Ogawa found the net for sixth-placed Vissel.