( CNN ) -- Both Roger Federer and Novak Djokovic were rattled at the World Tour Finals on Saturday but ultimately won their semifinals to set up a blockbuster . Federer saved four match points to inflict a devastating 4-6 7-5 7-6 ( 6 ) defeat on Davis Cup teammate Stan Wawrinka at the O2 Arena in London in easily the best match of a tournament that has featured an overflow of lopsided results . `` I 'm very lucky , '' Federer told the crowd . `` Stan played better from the baseline . I kept believing . I kept fighting . '' Wawrinka , now 0-11 on hard courts against Federer , will have to put the disappointment behind him as he 'll be on the same side as his more famous Swiss in next week 's Davis Cup final at France . Whereas Djokovic was n't happy with the crowd Saturday in his 6-1 3-6 6-0 win over Kei Nishikori , Federer was annoyed with French chair umpire Cedric Mourier . Having the momentum after breaking Wawrinka at love to end the second set , Federer thought he won the first point of the third set on his serve . But he apparently did n't hear Mourier overrule a Wawrinka ball originally called wide . When Wawrinka earned the next two points , the score went to 0-40 when Federer thought it was 15-30 . He aired his views to Mourier but the score stood and Wawrinka then broke . Even more drama unfolded later . Federer saved three match points at 4-5 in the third on Wawrinka 's serve and another on his own serve at 5-6 in the tiebreaker before converting on his first chance . It was the third time he saved match points this year , the other occasions coming against Gael Monfils at the U.S Open and Leonardo Mayer in Shanghai . A day after clinching the year-end No . 1 spot for the third time , meanwhile , Djokovic moved closer to another significant milestone at the World Tour Finals . If he defeats Federer on Sunday , the Serbian would become the first man since Ivan Lendl in 1987 to claim three consecutive titles at the elite year-end championships . Federer leads their rivalry 19-17 and triumphed in Shanghai but Djokovic has won 31 straight indoor matches . The 33-year-old Federer also played for nearly three hours Saturday and has significantly less time to recover . Djokovic would not have been the crowd favorite anyway , but his negative reaction when fans cheered a double fault in the second set against Nishikori might lose him more supporters . He replied by applauding sarcastically . `` The crowd has a right to do what they want , to cheer for whoever they want , '' Djokovic told reporters . `` ( There were ) some individuals that were going over the line throughout the whole match , some provocations that I usually do n't react on , but I did . `` It was my fault . I lost concentration . '' Nishikori had upended the world No . 1 at the U.S. Open in the last four on a sweltering September day , but Djokovic gained his revenge with an easy win indoors at the Paris Masters this month . The way Saturday 's affair started -- that , too , was an indoor duel -- it looked like a repeat of the Paris tussle . The exciting Japanese baseliner was hindered by a right wrist injury . Djokovic cruised in the first , needing a mere 22 minutes and dropping 11 points . When he broke in the first game of the second , this edition of the World Tour Finals was on course for an 11th straight-set result in 13 matches . Djokovic , however , double faulted for 1-1 and that was when the momentum shifted . Nishikori broke for 5-3 to the crowd 's approval with a winning forehand after Djokovic misplayed a smash and had his older rival in trouble to begin the third . `` I allowed myself to be in that situation to lose the set , maybe even lose the match , '' said Djokovic . `` Generally it was my fault and I should know better . '' Facing the second of two break points in the first game , Djokovic almost double faulted when he struck a heavy second serve . Later in the point , Nishikori misfired on a backhand down the line . It was the turning point of the set . Djokovic immediately broke for 2-0 and coasted , with Nishikori double faulting on match point . `` First couple points in the third set , I thought I had it , '' said Nishikori , the first Asian man to reach a grand slam final . `` I think I start thinking too much ( that ) he 's ( the ) No . 1 player , Novak . I think I risked too much . `` I think I did too many unforced errors first couple games . Then he started playing better . ''
Novak Djokovic defeated Kei Nishikori to reach the final at the World Tour Finals . Djokovic drops his first set of the tournament but prevails 6 - 1 3 - 6 6 - 0 in about 90 minutes . He will face Roger Federer in the final after Federer topped fellow qualifier Stan Smith . Federer saves four match points as he improves to 11 - 5 versus Wawrinka on hard courts .