Spain's Jon Rahm won the DP World Tour Championship
Koepka finished on 20-under 264 for the $1.8 million tournament at Phoenix Country Club in Miyazaki
It was also Grace's fourth Tour win on home soil
The world No.10 is tied with Patrick Rodgers and Patton Kizzire
No Chinese golfer, male or female, has ever topped the rankings before
Buhai shot a four-under-par 68 at Jian Lake Blue Bay Golf Club
The 14-time major champion has not played since February after a recurrence of back problems which forced him to miss the 2015-2016 season
The 29-year-old fired rounds of 64, 65, 74 and 68 for an aggregate score of 13-under 271
The supremely consistent 23-year-old American will advance to world number three with the win.
Ten of the world's top 30 will tee off on Jeju Island
He has been cleared by doctors to resume full golf activities
The 41-year-old has only played six competitive rounds in the past two years while trying to recover from multiple back surgeries.
The team will also take part in the Arab Championship in November
The four-time major winner will make history as the first woman to play on the European Senior Tour
A urine test revealed four other medications along with hydrocodone