NEW YORK -- Beyond their 20 Grand Slam singles titles, they have given so much to the game of tennis.
Following two surgeries on her foot and surviving blood clots and a hematoma, Serena wept upon her return to Wimbledon. On Wednesday, Venus withdrew from the U.S. Open, revealing that she had been diagnosed with Sjogren's syndrome, an autoimmune condition that caused her intense joint pain, a lack of stamina and, at times, overwhelming fatigue.
Venus spoke for the first time regarding her diagnosis, which she said came last month, with Elizabeth Vargas of "Good Morning America" on Thursday.
"Serena's conditions helped me to feel a new life on life in itself," she said. "So this, right now, I think will help me to feel grateful for everything that I have."
The headline, though, was that Venus will "absolutely" return to tennis, something that should surprise no one.
Later, she told The New York Times it would take three to six months for the medication to fully engage, which probably means she's done for the season.
Venus has battled through injuries many times and sounded confident since Sjogren's can be controlled with medication. The sisters have been pointing to playing doubles at the 2012 Olympics in London, and this confirms that is still a priority.
Interestingly, Venus said she has suffered the symptoms for years. However, the condition became more acute earlier this summer, making a correct diagnosis possible. A quick look through the archive finds a number of examples when she complained of fatigue, even as far back as 2007.
"I had swelling and numbness and fatigue, which was really debilitating," Venus said. "I just didn't have any energy. And it's not that you don't have energy; you just feel beat up.
"It's a huge relief because as an athlete everything is physical for me -- everything is being fit and being in shape. I think the best thing that could have happened for me this summer was to feel worse so I could feel better."
Serena, who remains the favorite in the tattered women's field, was in action Thursday against Michaella Krajicek. She did nothing to convince the pundits she won't roll through the rest of the field. The score was 6-0, 6-1, and it was over in 49 minutes. It was the fourth time here at the U.S. Open that Serena surrendered one game -- or fewer.
She now has lost all of three games in two matches and is 14-0 on hard courts since her comeback from a one-year sabbatical. How did she stay focused?
"It really wasn't that difficult, to be honest," Serena said. "[Venus] wants me to do my best and wouldn't want me to suffer. If anything, it should motivate me more."
Serena said she understands it is a genetic disease and hasn't experienced any of her sister's symptoms.
The Williams sisters have been a polarizing force since they came swinging for the fences out of Compton, Calif. They are adored by many and, it must be said, loathed by others.
Perhaps, two-time U.S. Open champion Tracy Austin said, the events of this summer might create something new. Empathy for the Williams sisters.
"That's what I'm feeling for them," said Austin, who like both women was ranked No. 1. "You look at what's happened to them, and it's pretty scary. But that's kind of life, isn't it?"
Austin, an analyst here for Tennis Channel, is intimate with the vagaries of life. A back injury at the age of 20 forced her to miss six years, but she came back to play two events in 1989. Then, on Aug. 3 in Short Hills, N.J., a car crash destroyed her right knee. Bone from her hip was grafted to the knee to make it serviceable.
Austin lifted her leg and tapped the ghastly scar.
"I was in the hospital for 11 days," she said. "Very quickly, it gives you a perspective. You see where tennis fits into your life."
And vice versa.
"It's a blessing for me to be here," Serena said. "OK, I had a blood clot or had surgery. Thank God, I don't have this other disease. Things can always be so much worse.
"You know a bad call here or there really is not the end of the world."
That is how far Serena seems to have come. Two years ago, a foot fault seemed very much like the end of the world.
"I know she's a fighter and she's really strong," Serena said of her sister. "I know she's really happy now that she knows what it is after all this time.
"If anything, that's going to help her now to treat it and go forward."
Said Venus, "Sjogren's is something you live with your whole life. The good news for me is now I know what's happening after spending years not knowing. I feel like I can get better and move on."
Greg Garber is a senior writer for ESPN.com.