Juan Martin del Potro beats Roger Federer to claim semifinal place in ATP World Tour Finals . Argentine 's straight - set victory ends the hopes of Saturday 's world No . 5 David Ferrer . Ferrer finishes on a high note as he beats Janko Tipsarevic in final round - robin match . I 'm the number four for sure . Federer will face Andy Murray in Sunday 's semifinals , while Del ##gado plays Novak Djokovic .
Juan Martin del Potro beats Roger Federer to claim semifinal place in ATP World Tour Finals . Argentine 's straight - set victory ends the hopes of Saturday 's world No . 5 David Ferrer . Ferrer finishes on a high note as he beats Janko Tipsarevic in final round - robin match . Federer will face Andy Murray in Sunday 's semifinals , while Del ##gado plays Novak Djokovic .