Nadal edges into Miami quarters

Rafael Nadal struggled to find his form as he scraped through to the quarter-finals at the Sony Ericsson Open in Miami, requiring two tie-breaks to overpower Stanislas Wawrinka 7-6 7-6.Second seed Roger Federer enjoyed a comfortable 6-3 6-2 win over American qualifier Taylor Dent to set up a clash against local favourite Andy Roddick.Britain's Andy Murray brushed past Serbian challenger Viktor Troicki in just 58 minutes, with a convincing 6-1 6-0 victory.Third-seed Novak Djokovic also advanced with a routine 6-3 6-2 win over Czech Tomas Berdych, setting up a quarter-final showdown with Frenchman Jo-Wilfried Tsonga, who rallied for a 6-7 6-3 6-2 win over compatriot Gilles Simon.