0700 GMT January 18, 2020
It meant back-to-back WTA Tour titles for the 21-year-old, who won the Australian Open in January, but then failed to match those high standards at the next three Grand Slams, AFP reported.
French Open winner Barty retains top spot and even extends her lead following the failure of Karolina Pliskova to get past the first round in China.
Osaka's rise to three means Elina Svitolina, quarterfinalist in Beijing, slips to four.
US Open champion Bianca Andreescu, who lost a thrilling quarterfinal to Osaka last week, also climbed a place to number five pushing Simona Halep down to six.
WTA Rankings as of October 7:
1. Ashleigh Barty (AUS) 7,096pts
2. Karolína Plíšková (CZE) 6,015
3. Naomi Osaka (JPN) 5,621 (+1)
4. Elina Svitolina (UKR) 5,525 (-1)
5. Bianca Andreescu (CAN) 5,041 (+1)
6. Simona Halep (ROU) 4,962 (-1)
7. Petra Kvitová (CZE) 4,776
8. Kiki Bertens (NED) 4,495
9. Serena Williams (USA) 3,935
10. Belinda Bencic (SUI) 3,848
Former world number one Andy Murray climbed over 200 places in the new ATP Rankings released on Monday while Novak Djokovic extended his lead over Rafael Nadal at the top.
Scotsman Murray, who is on the comeback trail after career-saving hip surgery, reached the quarterfinals of the China Open where he lost to eventual winner Dominic Thiem.
The run lifted the 32-year-old 214 places from 503 in the world to 289.
Djokovic's win in Tokyo at the weekend means the Serb is at number one for the 271st week of his career, one more than Ivan Lendl and trailing only Roger Federer (310) and Pete Sampras (286).
Djokovic heads to Shanghai Masters as defending champion while Nadal, his closest pursuer 1,140 points behind, has had to pull out with a wrist injury he picked up during last month's Laver Cup.
Thiem's victory over Stefanos Tsitsipas in Beijing sees the Austrian close to just 50 points behind the Russian Daniil Medvedev.
ATP Rankings as of October 7:
1. Novak Djokovic (SRB) 10,365pts
2. Rafael Nadal (ESP) 9,225
3. Roger Federer (SUI) 7,130
4. Daniil Medvedev (RUS) 4,965
5. Dominic Thiem (AUT) 4,915
6. Alexander Zverev (GER) 4,185
7. Stefanos Tsitsipas (GRE) 3,630
8. Kei Nishikori (JPN) 3,040
9. Karen Khachanov (RUS) 2,945
10. Roberto Bautista (ESP) 2,575