Kashima Antlers completed Japan's domestic double on Sunday by defeating Kawasaki Frontale 2-1 in the Emperor's Cup final in Suita.
Dos Santos secures cup in extra time
Kashima, who sealed their eighth J-League title last month, beat Kawasaki as Fabricio dos Santos Messias struck the winner in the fourth minute of extra time.
"All I was thinking was to help the team as a member and that led to the goal," the Brazilian midfielder told public broadcaster NHK. "I'm very happy."
"The players really wanted to win this title," added Kashima coach Masatada Ishii.
First side from Japan to make Club World Cup final
Two weeks ago, Kashima became the first Japanese team to reach the final of the FIFA Club World Cup after downing South American champions Atlético Nacional.
They lost 4-2 to Real Madrid in the trophy decider in Yokohama as Portuguese star Cristiano Ronaldo grabbed a hat-trick.