Simona Halep has retained her world number one ranking without stepping on court on Thursday after Madison Keys' withdrawal at the Internazionali d'Italia saw her reach the quarter-finals.

The Romanian could have been displaced by Caroline Wozniacki had she failed to reach the last eight and the Dane gone one round further than her.

But Keys had to pull out of their third-round contest due to a rib injury, giving Halep the walkover and ensuring she cannot be toppled at the summit.

Halep will face the winner of the match between Sloane Stephens and Caroline Garcia in the last eight.