They have celebrated triumphs together and yesterday one of the greatest double acts in sport departed Wimbledon en bloc, the Williams sisters obliged to share the desolation of defeat as they crashed out in the fourth round -- for the first time -- to straight-sets defeats.
The shock waves rippled through Wimbledon. If not the end of an era, it was certainly the diminishing of an aura.
There have been earlier individual losses but never have the pair been beaten at this stage, the greater of the upsets coming early in the afternoon as defending champion Serena went down 6-3 7-6 to France's Marion Bartoli.
Three hours later the sight of the Williams entourage turning on their heels and disappearing into the bowels of Centre Court told its own forlorn tale, Venus bowing out to Tsvetana Pironkova (23) for the second year in succession with a 6-2 6-3 defeat. The clan left the grounds abruptly.
The only previous champion left in the women's draw is Maria Sharapova.
The Williams girls do not appear to be cherished as much as they might. News of Serena's demise on Court No 1 was greeted with loud cheers on Centre Court.
A year of calamity for Serena ended with the biggest blow of all as she slumped to defeat in just under two hours. She has survived a clot on her lungs, a gashed foot and a high-speed fall from her bicycle, but even though she managed to save four match points against Bartoli, the defending champion could not hold out against her irrepressible opponent.
It was the four-time champion's first defeat at Wimbledon in almost three years and only her eighth in 12 years. For the first time since 2006, there will be no Williams in the final.
The younger Williams firmly rejected the theory that defeat meant inevitable decline, though.
"I don't know, like, I'm still here," said Serena defiantly. "I plan on doing better." There was no consolation to be had in the notion that had she triumphed after missing 47 weeks prior to the tournament with injury, it would have reflected badly on the quality of the women's game.
"Yeah, I'm super happy that I lost. Go, women's tennis," said Serena derisively, also dismissing the impression that she didn't appear as downbeat as she has done after previous defeats. "I'm more devastated than ever. I'm a much better actress now."
Bartoli, the ninth seed, revealed that she had been suffering from a stomach virus for five days during the opening week, causing her not just physical distress but also triggering a petulant outburst against her parents during a turbulent third-round win over Italy's Flavia Pennetta.
The pair, Walter and Sophie, were banished by their daughter from the courtside box after the opening set, a public humiliation.
"It was not something I was proud of and it has happened just once in 15 years," said Bartoli. "I had been sick, really sick for five days and I expressed my anger like that at the end of the first set which I lost. When you're not feeling well, then sometimes you do stupid things. It was great to have my parents here today and it definitely helped to have my dad there. I'm in the best shape of my life."
Williams' ability to overcome significant adversity in the build-up was always going to be stretched to breaking at some point. She had dropped sets in her opening two matches and her timing was out of kilter. But if there were doubts about her health and fitness, there could be no denying her heart.
Serena is a scrapper, a player whose best traits come out when she is under the most severe pressure. It showed as she fought to stay in the first set, saving three set points at 5-3, and only finally succumbing to a rasping ace.
Serena might have recognised something of herself on the other side of the net for there was controlled rage in Bartoli's ground strokes as well as an indomitable spirit. She has a quirky warm-up ritual before points, shadow-practising strokes.
Bartoli chased and scrapped and never held back from lashing winners. The only time she faltered was when holding two match points at 40-15 on her own serve. Glory beckoned, but Bartoli wobbled.
If she wilted then, allowing Williams to break serve, then the ensuing tie-break showed her mettle, Bartoli winning it 8-6.
Venus, at 31 the oldest competitor in the last-16 field, has also had her problems, missing five months through a hip injury. Despite beating the five-time champion last year, Pironkova has won only four matches this season. She has now won four in a row at this Wimbledon.
"Definitely, not our best day," said Venus. Quite. (© Daily Telegraph, London)