Brazilian attacker Caio gave Toninho Cerezo's men the lead in the 11th minute, before strikes from midfielders Shoma Doi and Yasushi Endo made sure of a comprehensive win for Kashima.
As a result, Kashima leapfrog Sanfrecce and previous leaders Vissel Kobe, who they were held to a 2-2 home draw by Cerezo Osaka.
A 78th-minute penalty from Marquinhos salvaged a point for Vissel after a double from Uruguay international Diego Forlan had turned the game in Cerezo's favour following Pedro Junior's opener.
Sagan Tosu are level on points with Kashima and Vissel thanks to an injury-time goal from Hiroyuki Taniguchi, which secured a 3-2 success at Nagoya Grampus.
Striker Kensuke Nagai looked to have earned Nagoya a share of the spoils when he equalised six minutes from time, only for Taniguchi to hit back and seal a dramatic win for Sagan in the third minute of added time.
Junya Tanaka also scored a stoppage-time winner as Kashiwa Reysol overcame Urawa Reds 3-2. The forward had earlier found the net from the penalty spot in an enthralling contest.
Bottom club Tokushima Vortis are still waiting for their first point of the season following a 2-1 home reverse against Albirex Niigata, their ninth consecutive loss since promotion to the top flight.
Yosuke Kawai scored the only goal of the game as Shimizu S-Pulse condemned second-bottom Velgata Sendai to a 1-0 defeat, while Omiya Ardija were beaten 2-0 at home by Ventforet Kofu.
Elsewhere, last year's runners-up Yokohama F. Marinos continued their poor start to the season with a 1-0 home loss against Tokyo and Kawasaki Frontale were 2-1 winners over Gamba Osaka.
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