Juan Martin Del Potro boosted his hopes of reaching the semi-finals of the Barclays ATP World Tour Finals with a crushing 6-0 6-4 victory over a below-par Janko Tipsarevic.
Serbian Tipsarevic has been struggling with illness and, after managing only four games against Roger Federer on Tuesday, he was clearly still less than 100% as he was brushed aside by Del Potro.
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.
The defending champion secured his progress from Group B earlier today with a straight-sets win over Ferrer.
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.
Tipsarevic at least stopped the rot in the opening game of the second set but he was constantly under pressure on his serve and cracked again in the fifth game.
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.