The world number one has put together one of the most impressive years in the sport's history and appears on course to win her 11th title of the season at the WTA Championships in Istanbul.
Williams posted her third comfortable victory of the round-robin phase, this time blasting past Petra Kvitova 6-2 6-3 to guarantee top spot in the red group.
Kvitova impressed in beating Agnieszka Radwanska in the first match and there was a feeling she may push the defending champion hard but that did not turn out to be the case.
Indeed, Williams' most challenging opponent might be her subconscious, with the 32-year-old revealing she is haunted by a tennis nightmare.
She said: "I have a recurring nightmare during grand slam finals. Not every time, but a lot of times.
"I dream that I'm in Australia and I leave the country to go do something in the States, and I don't make it back in time. And Venus has this nightmare, too.
"Wimbledon I had it a few times. It's very disturbing. It's just the worst dream ever, the worst way to lose a match."
Kvitova, who has failed to beat Williams in all five of their meetings, will still qualify for the semi-finals if she beats Germany's Angelique Kerber on Friday.
The Czech was fulsome in her praise of Williams, saying: "I think that she was really too good. And she had a great serve today. I think it was the big difference between us. I need to improve my serve for sure to compare to her.
"I'm still in the tournament and tomorrow is another day. I have still a chance to get to the semi-finals."
Kerber posted her first win at the WTA Championships with a 6-2 6-2 thrashing of Radwanska, whose record after a miserable week read six sets played, six sets lost.
In the white group, Li Na has one foot in the semi-finals but she knows there is still work to be done.
The fourth seed prevailed 6-3 2-6 6-3 over Jelena Jankovic in the first three-set match of the tournament.
It was Li's second victory from two round-robin games after she also beat Sara Errani, and the Chinese player is now in pole position to qualify from her section.
A set against Victoria Azarenka on Friday would put her through but a straight-sets loss would leave her extremely vulnerable.
Jankovic is still in a good position to reach the last four as well, knowing victory over the already-eliminated Errani in the final match would definitely be enough.