( CNN ) -- Tennis ' year-end championships are supposed to showcase the top eight players in the world but Monday 's opening matches in London took a backseat to another butting of heads between the two biggest names in the sport . The difference of opinion came as Stanislas Wawrinka beat Tomas Berdych 6-3 6-7 6-3 in the afternoon and Juan Martin del Potro defeated Richard Gasquet 6-7 6-3 7-5 in the nightcap . Having disagreed about a potential two-year ranking system and a previous selection of the ATP 's executive chairman , the latest dispute between Roger Federer and Rafael Nadal revolves around the surface for the World Tour Finals . Switzerland 's Federer says the tournament should remain on an indoor hard court but Spaniard Nadal wants it played outdoors and on surfaces including his preferred clay . Federer and his attacking game flourish under a roof -- he was unbeaten on indoor hard courts for two years from late 2010 -- and the 17-time grand slam winner boasts a career winning ratio of over 80 % when playing inside . Nadal 's indoor strike rate , meanwhile , stands at about 66 % -- and the world No . 1 has even less success on carpet . Clay is undeniably his most successful surface , with eight of his 13 grand slam triumphs coming at the French Open . Nadal has never won the ATP World Tour Finals while Federer has on six occasions , with four of those coming indoors -- Houston in 2003 and 2004 proving the exception . `` I believe it should be indoor and hard , '' Federer , president of the ATP Players Council , told CNN on Sunday . `` I know there 's an argument to have it on clay , on grass , to have it outdoors -- and I did play outdoors in Houston . `` I just feel indoors does n't have enough play . The indoor season is small . I believe indoors deserves a huge event , which this one is . '' Playing the tournament in such fashion is a natural extension of the European `` indoor swing '' that begins in the middle of October . Prior to London , Shanghai staged the year-end showpiece on an indoor carpet and then on an indoor hard court from 2005 to 2008 . The last time it was contested on a surface other than hard or carpet was way back in 1974 , on grass in Melbourne , and Nadal insists it is time for a change . The ATP , he says , should be `` fairer '' with the players . `` I know it 's not going to happen for my generation , '' Nadal , who stepped down as vice-president of the players council last year , told reporters on Monday . `` I 'm talking for the future generations , something that will be a little bit fairer for the players . And I think for the fans it will be interesting to change the surface every year to the surfaces we qualified on for the ( World Tour Finals ) . `` A good player has a chance to qualify for the ( World Tour Finals ) four or five times in his career , so if during this four years you have a different surface every year , a minimum one time he will have the chance to play on his favorite surface . '' In an interview with CNN last week , Andre Silva , tournament director of the World Tour Finals and the ATP 's chief player officer , said changing surfaces would make for an `` interesting concept '' but presented some problems . `` If it 's something the players want and can be done logistically , it 's something we can explore , '' said Silva . `` Even in the same place it would be pretty unique if you have all of a sudden one year on a hard court in London and the next year on a clay court . `` But it 's hard for players to switch surfaces . I think guys who have n't played on clay for six months would n't be comfortable going back to a surface they have n't experienced in six months . `` I 'm not opposed to it but I just think it becomes hard because of the logistics . '' When asked about the issue by reporters , Novak Djokovic -- the third most successful active player in the men 's game -- did n't `` know what to say rightly . '' The Serbian , however , said the championships should n't be held in the same city for more than three years . London 's stint will hit seven seasons come the end of its term in 2015 and Silva said there was `` definitely '' a possibility of a further extension . Federer told CNN he was n't opposed to the idea . On Tuesday , the Swiss enters the action when he meets Djokovic in the evening session with Nadal facing compatriot David Ferrer earlier in the day .
Tennis legends disagree on nature of ATP World Tour events . Roger Taylor argues the case for an indoor tournament while Murray wants an outdoor tournament . 2013 tournament got underway on Monday as Stanislas Wawrinka beat Tomas Berdych . Juan Martin del Potro rallied to beat Richard Gasquet in the evening session .