With his semi-final spot at the ATP World Tour Finals sealed up, Roger Federer will look to play spoilsport when the Swiss great takes on Juan Martin Del Potro.

Del Potro has had disappointments and happiness against Federer this season, with the agonizing loss to the 17-time Grand Slam champion at the Olympics one he would want to forget, while the Argentine got the better of the Swiss in Federer's home tournament in Basel a few weeks back.

Federer has already qualified for the last-four, and if he beats Del Potro he will qualify top of Group B, and will face Andy Murray. If the 31-year-old loses to Del Potro, then he has a chance of finishing second in the group, and a possible semi-final matchup against Group A winner Novak Djokovic.

Del Potro, who lost to David Ferrer in his first match, swept aside Janko Tipsaervic in his second, eliminating the Serbian with a lopsided 6-0, 6-4 win.

There are various possibilities that can come up with David Ferrer, who will face Tipsarevic in the late match, also capable of qualifying for the knockout rounds. So, Del Potro will look to end his match in two sets, to make his chances of qualifying much more easier.

"I'm glad to beat Janko," del Potro said on the ATP website after defeating Tipsarevic. "I play much better than my first match here. A win in two sets gives me a chance to go to the next match."

Del Potro faced a similar situation in 2009, when he needed a win against Federer to have a chance of qualifying to the semis. The big Argentine pulled off a three-set victory then to just about make it through at the expense of Murray.

On Saturday, he will be hoping for a similar result.

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