Rafael Nadal will end the year as number one after ATP World Tour Finals win over Stanislas Wawrinka Rafael Nadal has been playing down the importance of the No 1 ranking all year, saying that titles are what motivates him. But his body language betrayed a different story when he beat Stan Wawrinka on Wednesday to clinch his place atop the tennis mountain this Christmas. For the majority of this tense two-hour arm-wrestle, Nadal was uncharacteristically tentative. He was simply looping the ball back into the middle of the court, rather than whirling his racket with his usual piratical elan. But he still battled through to a 7-6, 7-6 victory, which he then celebrated with abandon. "This is one of the best things that I did in my career: coming back to the No 1 [position] after three seasons," said Nadal, who also finished top of the standings at the end of 2008 and 2010. That's very difficult in our sport, and after a very important injury. That's an emotional thing for me, for sure. Nadal also became the first man to secure a berth in Sunday's semi-finals here at the ATP Barclays World Tour Finals. Perhaps Wednesday's performance was not of a quality to indicate that he can win the event, but then the pressures were intense, with not only the prestige of the No 1 spot at stake but millions of dollars in attendant bonuses. Wawrinka should really have taken advantage but then he has something of a mental block against Nadal, a man he has yet to win a set against in 12 encounters. When he came into the interview room last night, Wawrinka was still seething about the many opportunities that had got away from him - as well as the on-court coaching that Nadal was receiving from his uncle, Toni Nadal. The umpire, Cédric Mourier, handed out a code violation in the first set but then did not follow up with the second warning that would have meant a point penalty. "We all know, players and umpire, that Toni is always trying to help Rafa," said Wawrinka. That's normal. That's part of the game. But when it's too much, it's too much. Before every point, he was trying to coach him.