Naomi Osaka became the first Japanese to win a Grand Slam singles title on Saturday as her idol Serena Williams angrily imploded, calling the chair umpire in the US Open final "a thief".

Osaka, 20, triumphed 6-2, 6-4 in the match marred by Williams's second set outburst, the American enraged by umpire Carlos Ramos's warning for receiving coaching from her box. When a second code violation for racquet abuse was handed out to her -- along with a point penalty -- Williams exploded.