Andy Murray says he needs to step up his performance if he is to beat Nicolas Massu today and keep his bid this week to become Britain's highest-ever ranked player going.

Murray needed three sets to beat Juan Monaco at the Sony Ericsson Open and now faces Chile's former Olympic champion, who is 91 in the rankings.

"He's a tough player," said the world No4. "I've only played him once on the grass at Wimbledon in 2006 and won that but I saw the end of his match against Mardy Fish on TV and it looked like he was playing well.

"If I want to win that one I'll have to up my game."

If Murray (above) wins the Miami event and world No3 Novak Djokovic fails to make the semi-finals then the players will swap rankings.

Murray's elder brother, Jamie, continues to struggle this season, despite linking up with a new partner, Swede Simon Aspelin. They lost 6-1, 7-6 to South African Rik de Voest and American Bobby Reynolds.

Dinara Safina and Ana Ivanovic crashed out of the third round in Miami with second seed Safina, of Russia, beaten 6-1, 6-4 by Australia's Samantha Stosur while the seventh seed from Serbia fell 6-4, 4-6 , 6-1 to Agnes Szavay, of Hungary.