Richard Williams, her father, said on Saturday that he had thought she was going to die. Just six months on, she is on course to mark her dramatic return with US Open glory.
The 29-year-old who has won 13 grand slams, returned to the tour in Eastbourne in June after a year out, first with a foot injury and then because of the clot.
After a slow start at Wimbledon, where she lost in the fourth round to Marion Bartoli of France, she won two titles this summer and at Flushing Meadows she has looked every inch the champion once again.
Even if the world No.1, Caroline Wozniacki, remains in the draw, with Kim Clijsters unable to defend her title because of injury and with an early defeat for Maria Sharapova, the title looks destined to go to the American for the fourth time.
The last time she was here in 2009, she left in disgrace after abusing a lineswoman on match point in her semi-final with Clijsters, the point penalty handing the Belgian a place in the final. Williams has not exactly been remorseful when discussing that moment here this year, but she has admitted she sees everything a little differently than she did before her illness scare.
“Tennis is great, I’ll take anything, but [her health] puts everything in perspective,” she said. “I love playing tennis, I love the battle, but I realise that life is so precious and things could be a lot worse. It isn’t all about tennis. It’s about life.”
Her tennis has certainly been impressive at Flushing Meadows and on Saturday she stepped up a gear when she beat the No.4 seed Victoria Azarenka 6-1, 7-6 to set up a fourth-round meeting with former world No.1 Ana Ivanovic today.
The first set was nothing sort of a masterclass from Williams as she dropped just eight points in the first five games.
However, she showed strong character to fend off a resilient Azarenka in the second set to clinch victory. “I think in the first set I played some really good tennis,” she said. “I think in the second set she played really, really good tennis. She kind of dictated and I allowed that. I probably could have played better in the second.
“It’s a good feeling, for sure [to play as well as she did in the first set]. I think every player wants to play that way but stay in that zone. I give her all credit. She totally lifted up her game and she totally started playing better.”
The standard of play in the second set was good enough to be a final -- something Williams admitted -- but she will not take a rejuvenated Ivanovic lightly. The Serb has just begun working with coach Nigel Sears, the former head of women’s tennis at the Lawn Tennis Association, and she is showing signs of getting back somewhere close to her form of 2008, when she won the French Open and became the world No 1.
“She’s playing well and she’s incredibly fit right now,” Williams said. “I just hate losing. I think sometimes when you lose it propels you to more wins.
“Like when I lost at Wimbledon, I was determined to do better. So it works.”
Venus Williams announced last week that she is struggling with an incurable disease that causes fatigue and muscle and joint pain.
Despite her being diagnosed with Sjorgen’s syndrome, she remains positive about returning to the game. If she needs inspiration, she only has to look as far as her sister.