By Martyn HermanSwitzerland’s challenge at the ATP World Tour Finals melted away like an Alpine glacier in a heatwave on Sunday as Rafa Nadal and Novak Djokovic marched on to the grand finale.Nadal muscled past Roger Federer 7-5 6-3 before Djokovic extended his hot streak to 21 consecutive victories with a routine 6-3 6-3 defeat of Stanislas Wawrinka.Fittingly the regular season will end with a $1.92 million shoot-out between the two dominant forces in men’s tennis who will go head-to-head for the 39th time on Monday night (10pm).Djokovic, who like Nadal had a 100 per cent record in round robin play, will be desperate to retain his title after ceding the world number one ranking to the relentless Spaniard in October.“We are both having a great season this year. This is probably the best possible final we have here in London. We’ll see what happens,” Djokovic, who was rock solid against tournament debutant Wawrinka, told a news conference.“This is probably the most competitive tournament that we have after grand slams in our sport, and we both want to end this season in the best possible way and end it with a title.”Predicting a winner will be a tough task.Australian Open champion Djokovic is unbeaten since losing the U.S. Open final to Nadal in September while Nadal, whose 10 titles this year include the French Open, hopes to cap an astonishing comeback following a seven-month injury lay-off.“The most important thing for me is that on the toughest surface for me, the most difficult one, I was able to win four matches against top-eight players,” Nadal, whose bulging CV is only missing a Tour Finals title, told reporters.“Now there remains one more match, probably the hardest, and I need to play my best match to have a chance.”Nadal boasted a 21-10 career record over Federer but Sunday’s victory was his first on the kind of indoor court that has proved problematic to the 27-year-old during his career.Former world number one Federer began in positive fashion, hardly dropping a point in his opening three service games and having a golden chance to break Nadal in the sixth game, only to send a wild forehand whistling over the baseline.“I went for it when I had a chance for a breakpoint in the first set. Maybe I shouldn’t have, but I did. No regrets there, I guess,” Federer, who has ended the year with a solitary title, his worst haul since 2001, told reporters.“I just struggled to stay consistent enough throughout the match, and that’s why he deserved to win. He was better today.”Federer offered hope to his fans when Nadal served for the opening set, winning a scintillating baseline exchange at 15-30 with a sweetly-timed forehand winner and scoring a break when his opponent ballooned a forehand out.It was one step forward and two back, however, for the 32-year-old who double-faulted in a poor service game to hand Nadal another chance to serve for the set and this time there was to be no reprieve.When a limp Federer forehand nose-dived into the net on break point at 2-2 in the second, the belief seemed to drain out of the Swiss and the end came quickly as Nadal maintained his stranglehold over the 17-time grand slam champion he has now beaten on eight of their last 10 matches.Nadal was typically generous, offering some encouraging words for Federer who has at least ended the year looking a little more like his old self having beaten Juan Martin del Potro and Richard Gasquet here.“I think he should be happier about the way he finished the season than compared how he was three months ago,” Nadal said.“I am sure today he was a little bit tired after the match of yesterday. I am sure that he will have the chance to start the next season in good condition and he will be one of the candidates to win in Australia.”It was left to Wawrinka to fly the Swiss flag but the world number eight ran into an unforgiving Djokovic.Wawrinka did slot away a volley to break Djokovic’s serve early on but was immediately broken back when he framed a forehand high into the rafters.Try as he might to get the ball past the elastic-limbed Djokovic, Wawrinka could not bludgeon his way through and another dropped service game put the Serb in control.Wawrinka, who twice pushed Djokovic to five-sets in the year’s standout matches at the Australian and U.S. Opens, held on grimly in the second set but could only applaud at one point as Djokovic somehow reached a certain winner and clawed a forehand across the bows of the in-rushing Swiss.Two breaks in the second set completed the Djokovic masterclass and a 14th consecutive win over Wawrinka.“I didn’t have enough energy today…against him, that makes a big difference,” Wawrinka said.