World No . 1 Roger Federer reaches semifinals of Estoril Open in Belgrade . Russian star , the 7-1 champion , overcomes slow start to beat Arnaud Clement . Federer Serbia Open title defense ends when he retires in quarterfinal . World No . 2 has been suffering with allergy and fatigue at his home event in Portugal .
World No . 1 Roger Federer reaches semifinals of Estoril Open in Portugal . Swiss star , the 2008 champion , overcomes slow start to beat Arnaud Clement . Novak Djokovic 's Serbia Open title defense ends when he retires in quarterfinal . World No . 2 has been suffering with allergy and fatigue at his home event in Belgrade .