Japan sparked in joy after Naomi Osaka won back-to-back Grand Slam titles at the Australian Open on Saturday, with fans taking pride in the feat that guaranteed she will become the country's first world No. 1 in tennis.In the namesake city of Osaka in western Japan, where she was born, around 30 fans waving Japanese flags erupted in joy after watching the grueling final match on an installed TV screen at a tennis center where Osaka practiced in her childhood.Osaka wins Australian Open, second straight Grand Slam titleComposure on big stage fuels Naomi Osaka's rise to top"I'm deeply moved. I…READ FULL ARTICLE