The story has been going for more than a decade now but once again the final of the Sony Ericsson WTA Tour Championships will be the exclusive domain of the Williams sisters. And for one crucial reason; they are still the strongest players in the woman’s game and this week Venus and Serena have also proved to be the most durable.

It really was a case of fittest players left standing as the top eight of the women’s tour played out their calendar-ending finale for the second time in a three-year stay in Doha. A year ago Venus came out on top but now she must take on sister Serena for the second time in less than a week to reclaim her crown and prove that despite being the oldest player in the event, she is also the most overworked.

Sunday will see the 23rd meeting of the sisters and Serena, a 5-7,6-4,7-6 winner in their round-robin meeting on Wednesday, holds a 12-10 lead after also coming out on top in this summer’s Wimbledon final. Good fortune came her way as Caroline Wozniacki, who has been struggling to stay on court for most of the week after taxing her 19-year-old body to the limits of exhaustion, was forced to retire from the semi-final while trailing 6-4, 0-1. All week the Dane had been struggling with a hamstring injury but in the end a nagging abdominal strain forced her to quit.

She joined the list of spent women to submit to the pains brought on by a longm, competitive season. The deposed world No 1 Dinara Safina could play only two games before she realized the pain in her back was too much; Victoria Azarenka tested herself to the limit before quitting against substitute Agnieszka Radwanksa and then came Wozniacki’s pain-wracked farewell.

Serena, guaranteed to end the year with the No 1 ranking showed an unusual compassionate side. Offering consolation to Wozniacki, she said: “Caroline wasn't doing that great but I wasn't playing great. I think it's hard to play well against a player who's injured and is so nice. It was really a tough battle out there.”

Serena is playing with a leg injury which has forced her to withdraw from next weekend’s Fed Cup final against Italy. “I'm trying,” she insisted. “I'm doing the best I can. That's all I can do. Win, lose or draw, I'm literally just giving everything I have but I think I'm just going to be wiped out by the end of this tournament.”

Venus certainly had to battle her way through to the final again the hard way after playing seven hours and 52 minutes of tennis in the round-robin stages. All four of her matches have extended to the maximum three sets and after requiring on-court treatment to the knee that has troubled her for most of the second half of the year, she fought on to register victory over Jelena Jankovic in the first semi-final, 5-7 6-3 6-4, in two hours 33 minutes.

Several of her younger rivals have been reduced to tears this week as the physical demands of the season took their toll, but Venus is made of tough stuff. Admittedly the tennis was neither very pretty or indeed of a particularly high standard as unforced errors proliferated and both girls found breaks of serve easy to negotiate.

Jankovic could really have been termed a fortunate semi-finalist. She was the last to qualify for the event and after losing her initial match, she then benefited from Safina’s retirement with back problems.