Rafael Nadal of Spain celebrates winning against Tomas Berdych of Czech Republic during their men's singles tennis match at the ATP World Tour Finals at the O2 Arena in London, Nov 8, 2013. [Photo/Agencies]

LONDON - If Stanislas Wawrinka's life depended on the outcome of one tennis match he would surely want Rafa Nadal fighting his corner, and while the stakes were not as high as life or death on Friday the Swiss player's fate was in safe hands.

Having beaten David Ferrer 6-7(3) 6-4 6-1 to claim his second Group A victory at the ATP World Tour Finals, Wawrinka knew a Nadal win later against Czech Tomas Berdych would send him through to the semi-finals along with the Spaniard.

Nadal was already guaranteed his place in the last four but any thoughts of the Mallorcan going through the motions and conserving energy were quickly dispatched as the world number one went about his work with his usual intensity.

Berdych pushed the 27-year-old all the way and thundered through the second set in 29 minutes but Nadal pulled out all the stops to earn a 6-4 1-6 6-3 victory, sealing top spot in the group and avoiding a semi-final clash with Novak Djokovic.

"At the end I play for myself, 200 (ranking points)," Nadal said when asked about the implications of his win for Wawrinka.

"I went on court like as if I am playing for the qualification. I knew (after winning the first set) that I had won the group, but it was important to finish that match the way that I did. I'm very happy for that," added Nadal, who is still in line to earn the $1.9 million for an undefeated champion.

Wawrinka has the daunting task of trying to derail Djokovic's bid to retain the title but the Swiss will not care.

The 28-year-old was the only first-time qualifier at the tournament and with wins against Berdych and Ferrer he has proved he belongs in such exalted company.

Even in losing 7-6 7-6 to Nadal he played superb tennis, actually winning more points than the Spaniard, and Djokovic will be wary of his threat, especially after their epic tussles at the Australian and US Opens this year.

"I can be only really happy with the tournament. It doesn't matter what happens tonight," Wawrinka had told reporters after beating Ferrer, although he admitted he would be glued to his television later rooting for Nadal.