Novak Djokovic continues his quest to regain the world No 1 ranking with a World Tour Finals semi-final showdown against Kei Nishikori. The Serb saw his 122-week grasp at the top of the rankings ended by Andy Murray in Paris almost a fortnight ago, but he can reclaim the position depending on the outcome this week.First he must overcome Japans Nishikori and with a dominant 10-2 record in the head to head he will start Saturdays semi-final in confident fashion, especially after a week that has seen him return to somewhere close to top form. Novak Djokovic and Kei Nishikori have met in two finals this year - on Saturday they meet for a place in the World Tour Finals showpiece Djokovic lost his opening set of the week to Dominic Thiem last Sunday but recovered to win the match in three sets and followed up with another pair of victories over Milos Raonic and alternate David Goffin,He had to come through an epic content against Raonic, eventually prevailing 7-6 7-6 while he had little trouble against late replacement Goffin who was dispatched 6-1 6-2.Nishikoris last four place had already been assured after Murrays straight sets win over Stan Wawrinka earlier in the day. Having begun the week with a superb victory over Wawrinka, Nishikori lost his next two matches.Having pushed Andy Murray close in his second match before losing in three sets, he ended the group stages with another three-set defeat, losing to Marin Cilic in three sets on Friday night. World Tour Finals - Story So Far Novak Djokovic Kei Nishikori beat Dominic Thiem 6-7 6-0 6-2 beat Stan Wawrinka 6-2 6-3 beat Milos Raonic 7-6 7-6 lost Andy Murray 7-6 4-6 4-6 beat David Goffin 6-1 6-2 lost Marin Cilic 6-4 2-6 3-6 John McEnroe talks about the price of ending the year as the world No 1 While world No 5 Nishikori has been in fantastic form this season, reaching his second and third Masters finals as well as his second Grand Slam semi-final, he will have to overcome a run of form against Djokovic that has seen him lose his last nine matches against the Serb.Djokovic has won all five of their meetings this year, including victory in both the Canada and Miami Masters finals, while Nishikori has won just three sets in their contests since his last win, a memorable US Open semi-final success in 2014. Kei Nishikori has come as close as anyone to beating Andy Murray this week, losing in three sets in the group stage The pair have twice met at the O2, Djokovic winning in the group stage in both 2014 and last year where he was a 6-1 6-1 victor.The signs are ominous for Nishikori but the 26-year-old appears to be relishing the challenge against the very best these days and a win would see him beat his semi-final performance of his World Tour Finals debut a couple of years ago. Djokovic v Nishikori met in the Miami final earlier this year Djokovic v Nishikori met in the Miami final earlier this year As ever it will be a doubles match which kicks off the evening and after confirmation of their world No 1 ranking, Jamie Murray and Bruno Soares will hope to book a final place when they face Rajeev Ram and Raven Klaasen.Murrays position as the year-end No 1 was confirmed when the French pairing of Nicolas Mahut and Pierre-Hugues Hubert lost their third group game of the week on Friday.Murray and Soares claimed the Australian and US Open titles and have won two of the three matches the pair have played.Follow all the action from the O2 on Saturday when the action begins on Sky Sports 3 from 12pm and 4pm or via our live blog here at www.skysports.com/tennis. Also See: World No 1 permutations Djokovic hammers Goffin Cheap Shoes From China . 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RIO DE JANEIRO -- Men and women in skimpy swimsuits frolicked in the surf, sprawled out on towels or kicked around a soccer ball at Copacabana Beach. Others cooled themselves under an umbrella at one of the many open-air kiosks serving food, beer and the local sugar cane cocktail, caipirinha.Inside the Olympic beach volleyball venue, the atmosphere was only slightly less festive.With a DJ spinning a samba beat and thousands cheering on their hometown teams, the Olympics sexiest sport returned to its spiritual home on Saturday for an opening session that brought out the best the beach has to offer.Defending champion Kerri Walsh Jennings and her new partner, April Ross, easily won their opening match with a 21-14, 21-13 victory over Australia that began at 12:34 a.m. and took just 35 minutes. Fellow Americans Casey Patterson and Jake Gibb also won their opener, beating Qatar 21-16, 21-16 on a day U.S. Secretary of State John Kerry visited the venue (as did Italian Prime Minister Matteo Renzi).Fans sang, waved their flags and cheered on their teams for the four matches on a sun-baked morning at the temporary stadium erected on this citys signature strip of sand. (Two more were to follow in the afternoon and evening.) Players kicked up sand as they dived for the ball, celebrated points with hugs and high-fives, and invariably saluted the crowd when walking off at after their matches.I love South American fans, and I love how the people love sports, said Argentinas Georgiana Klug, who lost her opener with Ana Gallay, falling to Spain in straight sets. All the singing, dancing -- it makes me feel like home.Beach volleyball joined the Olympic program at Atlanta in 1996, but for most Summer Games the venue has been built in a park (or parking lot), with thousands of tons of sand trucked in to create the playingg surface.dddddddddddd For the first time since Sydney in 2000, the sport is returning to an actual beach.And theres none more fitting.With the party ready to start both in and outside the arena, Italian Adrian Carambula got things started with his trademark Skyball, a high and spinning serve that wanders into the path of the sunshine and wind and confounds attempts at a return. Although he typically uses it sparingly, Carambula said he was egged on by his friends to start things off with a little flair.They said they wouldnt talk to me if I didnt, he said in a post-match interview that was twice interrupted because the prime minister asked him to come over and pose for a picture.My legs were shaking before the first serve, said Carambula, who with Alex Ranghieri beat Clemens Doppler and Alexander Horst 21-14, 21-13. When I walked in I actually got a little bit emotional. I wasnt expecting it, but I embraced it and I played with it. So very special.The biggest crowd -- and the most vocal support -- was for Brazils reigning world champions Alison and Bruno, who beat Canada in a straight-set but razor-thin 21-19, 22-20 victory. In the morning sessions other match, Austria beat Costa Rica in straight sets.In the afternoon, Brazils Agatha and Barbara needed three sets to get past the Czech Republic; the Dutch men beat Russia in straight sets and the women did the same to Venezuela.In the early part of the night session, the Spanish men beat Austria and Poland beat Germany. China held off Switzerland in a match that had to resume after a challenge on match point was reversed.---Jimmy Golen has covered Olympic beach volleyball since 2008. Follow him at http://www.twitter.com/jgolen ' ' '