ATP World Tour Finals 2013: Rafael Nadal secures end of year world No 1 ranking with victory over Stanislas Wawrinka

The Spaniard needed to win two games at the O2 to ensure he wasn't surpassed by Novak Djokovic

Rafa Nadal at the O2 (GETTY IMAGES)

Rafael Nadal booked his place in the semi-finals of the Barclays ATP World Tour Finals and secured the year-end number one ranking with a hard-fought victory over Stanislas Wawrinka at London's O2 Arena.

Novak Djokovic had kept the ranking race alive going into season-ending tournament with a run of 17 straight victories but Nadal still knew two wins in London would be enough to give him the honour for the third time.

It is a remarkable achievement given Nadal did not play a tournament until February after seven months out with knee problems.

Many questioned whether the Spaniard would be able to hit the same heights but he has put together one of the best years in tennis history, winning 10 of his first 13 tournaments.

He has found the going a bit tougher since winning his 13th grand slam title at the US Open but was an easy winner over David Ferrer in his opening round-robin match.

That meant a straight-sets win over O2 debutant Wawrinka would send him through to the semi-finals, and the omens were good given he had won all 24 of their previous sets.

Wawrinka has come close to breaking that run on a few occasions, including in Shanghai last month, when he had a point to win the opening set.

It was a similar story here but once more it was Nadal who prevailed, this time in two tie-breaks, to win 7-6 (7/5) 7-6 (8/6).

Nadal was rock solid to start with, not making a single unforced error in the opening seven games and breaking Wawrinka to lead 3-2 when the Swiss double-faulted.

But Wawrinka has had the best season of his life and he continued to take the fight to Nadal, earning his reward when the top seed served for the set at 5-4.

Nadal picked up a code violation for taking too long between points and Wawrinka finally managed to breach his defences.

Nadal was on the defensive again in the tie-break but, as he has so often done in his career, kept the ball coming back over the net and a stumble from Wawrinka as he came into the net on set point proved his undoing.

It was no wonder the 28-year-old was frustrated and he smashed his racket three times before flinging it angrily away.

The second set began in a similar fashion, Wawrinka unable to take his chances while Nadal seized his to lead 4-1.

Back came Wawrinka, though, finally taking a break point with a volley that caught the top of the net but landed in.

Another tie-break would decide the set and Wawrinka had a chance to level up after fighting back from 4-1 down.

But Nadal saved the set point expertly and two errors from Wawrinka settled the match in the Spaniard's favour, even though he won three fewer points.

Wawrinka, who beat Tomas Berdych in his opening match, is still in a decent position to reach the last four ahead of his final group clash with Ferrer on Friday.

PA