Day 6: Federer v Del Portro

Sue Barker presents live coverage from London's O2 Arena as the group stages at 2013's ATP World Tour Finals draw to a close. Sixth seed Juan Martin del Potro beat Roger Federer to progress through to the semi-finals, along with the great Swiss player 12 months ago, edging out fourth-seed David Ferrer for qualification on a dramatic day of action.