The Romanian, who lost to world number one Serena Williams in the final on Sunday, nudges back ahead of Maria Sharapova, who missed the tournament due to injury and who has been sidelined since a semi-final loss at Wimbledon in early July.
Read: Serena captures 2nd straight Cincinnati title
Former world number one Caroline Wozniacki completes the top four with the start of the US Open, the final Grand Slam tournament of the season, just a week away.
Williams, who is more than double the points ahead of Halep in the rankings will be out to sweep the Grand Slam tournaments in New York, emulating Steffi Graf in 1988.
1. Serena Williams (USA)
2. Simona Halep (ROM)
3. Maria Sharapova (RUS)
4. Caroline Wozniacki (DEN)
5. Petra Kvitova (CZE)
6. Lucie Safarova (CZE)
7. Ana Ivanovic (SRB)
8. Karolina Pliskova (CZE)
9. Garbine Muguruza (ESP)
10. Carla Suarez Navarro (ESP)
The newly revealed male ranking didn't witness much change, just some reshuffling as Roger Federer and Andy Murray switched spots.
Read: Federer downs Djokovic for seventh Cincy title
1. Novak Djokovic (SRB)
2. Roger Federer (SUI)
3. Andy Murray (GBR)
4. Kei Nishikori (JPN)
5. Stanislas Wawrinka (SUI)
6. Tomas Berdych (CZE)
7. David Ferrer (ESP)
8. Rafa Nadal (ESP)
9. Marin Cilic (CRO)
10. Milos Raonic (CAN)
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