Laura Robson will take over from Heather Watson as the British number one next week after making a winning start at the Family Circle Cup in Charleston.
Robson, 19, had a straight-sets win over Estrella Cabeza Candela yesterday despite experiencing problems with her serve.
She committed eight double faults and struggled to put her first serve in play but was not punished by her low-ranked Spanish opponent and clinched a 6-2 6-2 first-round victory at the clay-court event.
Robson began the week at 42nd in the world rankings, which will be next updated by the WTA on Monday, two places behind Watson who is sitting out the tournaments in Charleston and Monterrey. She knew it would take only one win to overtake her compatriot and Fed Cup team-mate.
The Briton broke her opponent's serve five times and finished off with a big forehand winner, and will be seeking to go a step further in the tournament today when she faces Canadian qualifier Eugenie Bouchard in the second round.
Robson is coming off the back of a strong doubles showing at the Sony Open in Miami, where she reached the final alongside America's Lisa Raymond.
Defending champion Serena Williams is the top seed in Charleston, with Robson the 16th seed.