Robson climbs to No 1 slot

The Wimbledon girls' champion Laura Robson has taken over as the world's top-ranked junior. The 15-year-old succeeds Thailand's Noppawan Lertcheewakarn, whom she beat in the final at SW19 last July.

The Wimbledon resident is currently at a career-high senior ranking of 499, making her the British No 13. In Miami, the world No 1 Serena Williams struggled to a 7-5, 5-7, 6-3 win over China's Zheng Jie to earn a place in the quarter-finals of the Sony Ericsson Open. Serena's sister Venus came from a set down to beat Poland's Agnieszka Radwanska 4-6, 6-1, 6-4.