If any further evidence is needed to forever silence the conspiracy theorists who maintain the outcome of matches between the Williams sister are decided in advance, then this was perfect. If family policy was to ensure both made it through to Saturday’s semi-finals of the Sony Ericsson WTA Tour Championships then certainly Serena would have been celebrating victory.

Instead she was left tearful and tormented by Venus, and forced to rebound immediately from the most emphatic drubbing in the ten-year-long 18-match series of these two champions started playing against each other competitively. More than once Serena has admitted to losing her cool on court but never before have spectators been confronted with the sight of her in such distress mid-match with tears of frustration streaming down her face.

Venus progresses with a three wins from as many outings in her initial round robin group but Serena must beat Elena Dementieva if she is to survive. Though the Russian is notoriously brittle in this tournament, she regrouped some of her self-confidence by repeating her Olympic final superiority over fellow Muscovite Dinara Safina and if Serena is as inept and bereft of any creditable tactics as she was in the second two sets of her 5-7, 6-1, 6-0 thrashing then she will be in trouble.

Serena lost the last nine games in succession and was unsuccessful in 12 of the last 13. Never before has one sister registered what the Americans refer to as a bagel and the rest of the tennis world call simply a 6-0 set against the other. Clearly the humiliation of the experience was tough to take.

“This was definitely the worst match I've played this year by far,” said Serena in a mode of near apology. “I didn't even look like a top eight player. Maybe top 600 in the juniors perhaps. I just couldn't keep a ball in play. I couldn't keep more than two balls over the net. I couldn't serve. I couldn't hit a backhand. I couldn't hit a forehand. I couldn't even volley.

“I don't think I've ever played like that. I mean, I've never been in a situation where I just feel like I can't do anything. Just everything was off and it was very frustrating out there. It was just terrible, terrible, terrible tennis.”

Not all of Serena’s self-criticism is accurate. She did manage to deliver nine aces compared to her sisters six but this statistic should be tempered by the fact that the double fault count was nil to six in Venus’ favour. After an undistinguished but nevertheless closely contested first set the momentum swung completely in Venus’ direction thereafter and never changed except for the fact Serena’s late resistance saved three match points.

But this most certainly was not the performance of a champion many believe is the most overpowering female player ever to pick up a tennis racket. At this year’s Wimbledon final Serena was insistent that her inability to maintain mental control cost her dearly but this was a different matter altogether.

Although Venus is a fierce competitor and a proven winner, she garnered no real satisfaction from seeing her sister in such distress. “It wasn't the happiest match,” she maintained. “I think she started to get a little more impatient, a little more upset with her performance and then just let it go.

“I think out of all the players on the tour I probably respect her game the most. So it's a little bit tougher to play against someone that you respect so much.”

And so the Williams sisters left the Khalifa International Stadium together and headed back to their luxury hotel. Fortunately for Serena they left long before Dementieva had registered her 6-2, 6-4 win that ends a losing streak of ten matches in this calendar ending event.

What the conversation was in the Williams’ courtesy car we shall never know. Similarly we will never be party to their pre-match conversations over the breakfast table but on the basis of what was seen in this latest encounter any theories of collusion now seem folly.