Doha, Nov 7: Venus Williams made certain of reaching the last four of the WTA Championships with a landslide 5-7, 6-1, 6-0 victory over sister Serena Willia ms on Thursday.
The result brought the first love set between them in any of their 18 WTA Tour matches and twice reduced the younger sibling to tears.
The Wimbledon champion's win over the US Open champion was her third in three days, enabling her to finish her top of her round robin group, and ensuring that she joined Jelena Jankovic and Vera Zvonareva in the knock-out semi-finals of the women's season-ending event.
But Serena, who has only one win, will need to beat Olympic champion Elena Dementieva on Friday if she is to be sure of keeping alive the chances of an all-Williams final.
"I couldn't keep a ball in play," Serena said. "I couldn't keep more than two balls in play. I have no idea why.
"I have never played like that before. I have never been in a situation where I can't do anything. I was very, very frustrated."
So much so, that from 1-2 in the second set she lost ten games in a row, her eyes welling up at 0-3 in the final set and then again at the end as she walked back to the chair.
As she became increasingly confused, she played worse and worse, and her indecision about taking a ball twice confused a ball boy, making some of the crowd laugh.
But the only time Serena gained the relief afforded by a sense of humour was afterwards when she said: "I didn't look like a top eight player - maybe top 600 in the juniors." Her own eloquence about the disaster made her grin.
Venus admitted that her pleasure in playing well was tempered by her sympathy for her sister. Asked what she might be able to do to help her, she said: "There is nothing I can do.
"She just has to figure it out in her head as in the other matches, even though this one was against me. So she just has to take some time and she will come out stronger."
Venus has never made the final of this event, and much may depend on her fitness, and especially the condition of a knee, which she several times touched. Asked about it, she said: "I am doing okay," but declined to elaborate.
Earlier world number one Jelena Jankovic made sure that she would qualify for the semi-finals for the first time when she survived a first set wobble and a neck-and-neck second set to beat Svetlana Kuznetsova, the former US Open champion.
The Serb's 7-6 (8/6), 6-4 victory over the Russian also made sure that Vera Zvonareva, the Russian who was the last to qualify for the eight-player finals, would also make it - far more unexpectedly - to Saturday's semis.
Both players have two wins, which means that neither Kuznetsova, who had the weapons to succeed but made mistakes which meant she was too often playng catch-up, nor Ana Ivanovic, the former world number one, can now qualify.
It clearly meant a lot to Jankovic, who is enduring the sniffy reaction to having become year-end world number one without having won a Grand Slam, and has increased her chance of answering it by winning the biggest title of her career.