Twenty-year-old Naomi Osaka won her first Grand Slam title, defeating her idol, Serena Williams, in a bizarre and memorable U.S. Open final that descended into spectacle when Williams angrily protested several penalties she was issued.

Osaka was in firm control of the match—a generational showdown between an emerging star and perhaps the game’s greatest champion—when Williams spiraled into a series of confrontations with the match’s umpire.

The...