Kashima Antlers and Yokohama F. Marinos were left as the only J.League clubs with a perfect record after they recorded comfortable wins.
Takeshi Aoki fired Kashima ahead on 40 minutes before second-half goals from Shoma Doi and Yuta Toyokava condemned Tosu to their first defeat.
Yokohama were sent on their way to a third win in three by Seitaro Tomisawa after 14 minutes. Sho Ito and Jungo Fujimoto completed the scoring after the break.
Defending champions Sanfrecce Hiroshima dropped their first points to complete a forgettable week.
Sanfrecce lost 2-1 at Central Coast Mariners in the AFC Asian Champions League in midweek and goals from Shinzo Koroki (42) and Genki Haraguchi (90) condemned them to a 2-0 defeat at home to Urawa Red Diamonds.
Ryota Moriwaki saw red for Urawa in injury-time.
Kosuke Kikuchi levelled at 3-3 before Cheol Cho-young won the game.
Kikuchi had scored the opener after four minutes before Tomoki Imai's own goal cancelled it out.
Akihiro Ienaga sent Omiya back ahead on 29 minutes before Renato (70) and Yoshito Okubo (86) seemingly grabbed the win for Kawasaki. Their midweek trip to Ulsan Hyundai apparently caught up with them though as Omiya stole the points.
The game was level when Genki Omae's 23rd-minute penalty cancelled out a 15th-minute Yusuke Maruhashi opener. Cerezo stormed away thereafter with goals from Tatsuya Yamashita, Gojko Kacar and Kenyu Sugimoto.
Australia striker Josh Kennedy struck the only goal on 66 minutes as Nagoya Grampus beat Kashiwa Reysol 1-0.