US Open winner Bianca Andreescu, 200th in the world rankings a year ago, leapt into the top five on Monday, while Ashleigh Barty knocked Naomi Osaka off top spot.
Eliminated in the first qualifying round in New York a year ago, Andreescu rose 10 places to No 5 after beating Serena Williams in the final on Saturday.
The 19-year-old Canadian is one place behind Osaka, whose defence of her US title ended in the quarterfinals.
Barty was also knocked out in the last eight but, since she was knocked out in the fourth round in 2018, increased her ranking points total.
The Australian is just over 400 points ahead of the Czech Karolina Pliskova, who climbed one place to second.
The top two have opened a substantial gap over Elina Svitolina, who rose two spots to third after reaching the semifinals in New York.
RANKINGS AS OF SEPTEMBER 9:
1. Ashleigh Barty (AUS) 6 501 pts (+1)
2. Karolina Pliskova (CZE) 6 125 (+1)
3. Elina Svitolina (UKR) 5 032 (+2)
4. Naomi Osaka (JPN) 4 846 (-3)
5. Bianca Andreescu (CAN) 4 835 (+10)
6. Simona Halep (ROU) 4 803 (-2)
7. Petra Kvitova (CZE) 4 326 (-1)
8. Kiki Bertens (NED) 4 325 (-1)
9. Serena Williams (USA) 3 935 (-1)
10. Belinda Bencic (SUI) 3 738 (+2)
