New US Open champion Naomi Osaka can become Japan's first world number one, says Japanese former Grand Slam semi-finalist Kimiko Date.
The 20-year-old's straight-sets win on Saturday was overshadowed by Serena Williams' outbursts at the umpire.
But Date said Osaka's triumph in her first Grand Slam final was "amazing".
"If she continues to develop the way she has over the past two weeks, she can go on to be Japan's first world number one," added Date.
"To keep your cool like that, from the moment you step onto court to the last point, isn't easy.