Juan Martin Del Potro brushes aside below-par Janko Tipsarevic at World Tour Finals Del Potro, from Argentina, lost to David Ferrer in his first match so badly needed a good win to keep him in contention, and he will reach the semi-finals if he beats Federer in two days' time. Del Potro, who was watched by friend and Manchester City striker Sergio Aguero, had never lost a set against Tipsarevic in three previous meetings and immediately set about maintaining that record with a run of six straight games. To the 28-year-old's credit, he continued fighting to the last and forced Del Potro to serve it out, but that proved to be no problem for the Argentinian, who wrapped up victory in an hour and 16 minutes. The defeat ended Tipsarevic's hopes of making the semi-finals at the tournament for the first time, but he was grateful for small mercies, saying on Twitter: "Passed the one hour mark one more time baby!!!!Wooooohooooo!!!;) " Del Potro, meanwhile, gave the crowd a little bit of extra entertainment after the end of the match as he Aguero knocked up on the O2 court.