An Extraordinary Performance to Reach an Even Rarer Matchup

They were once awkward occasions met with an ambivalent mix of curiosity and sympathy. But it has been so long since tennis had an all-Williams match for high stakes that perhaps the sport and the sisters are finally ready to embrace the prospect instead of keeping it at long arms' length.(Serena Sets up Match vs Venus)

It is an against-the-odds development that this fourth-round family affair will happen at all, considering that Serena Williams was twice two points from defeat against Heather Watson on Friday before prevailing, 6-2, 4-6, 7-5.

"How I pulled through, I really don't know," Serena Williams said of her latest great escape.(Serena Wants Fans to Support Venus)

And it is, of course, against the odds that she and her sister Venus are still playing with the kind of skill, stamina and commitment required to reach the second week at Wimbledon at this stage of their lives.

Venus Williams, who defeated Aleksandra Krunic, 6-3, 6-2, on Friday, just turned 35 and has long had an autoimmune disease, Sjogren's syndrome, that can leave her sapped of energy, sometimes without warning.(More Gains for Americans on Day With More Upsets)

Serena Williams will turn 34 in September and has had injuries and a major health scare of her own, needing emergency hospitalization after a pulmonary embolism in 2011.

The sisters already have their millions of dollars and their five Wimbledon singles titles apiece. Raised to be champions before they had any say in the matter, the sisters have endured and excelled of their own free wills like no other women of their tennis generation.

"The message is enjoy them while we've got them," said David Witt, Venus Williams' longtime hitting partner and coach. "You'll never see something like this again."

It is hard to disagree as they prepare to play Monday at Wimbledon, their first meeting at a Grand Slam tournament since the 2009 final here, which Serena Williams won in straight sets.

This Wimbledon match will be in the round of 16, making it their earliest meeting in any regular tournament since the 2005 U.S. Open. And if a ball or two had landed in different places Friday, it could so very easily have been Venus Williams facing the unseeded Watson instead.

Serena Williams has been walking a tightrope at the Grand Slam tournaments all season, and though she has done plenty of tottering on high with her racket in hand, she has yet to tumble and remains in position to complete the first Grand Slam since Steffi Graf in 1988.

Watson, a quick and resourceful 23-year-old from Britain who once had a poster of the Williams sisters on her wall, was the latest would-be spoiler.

After losing what seemed to be a routine opening set against the much more powerful Serena Williams, Watson gradually adjusted to the pace and the occasion. She played clever tennis, mixing tactics and spins and, above all, playing outstanding, corner-to-corner defense against Williams' increasingly overwrought onslaught.

Watson, in her first match against Williams, eventually found herself serving for the match at 5-4 in the final set and twice reached deuce on her serve in that game.

But Williams, the world's No. 1 player by a wide margin, again found a way to wriggle free. The effort, the emotion and perhaps the cumulative effect of all her tight matches this season appeared to leave her more drained than elated.

"There was a few points that could have gone either way," Watson said. "I just feel like when she needs to hit the line or needs to hit a winner, she'll just do it, and that's what she did."

Williams, despite having played in 16 Wimbledons, had never faced a British player here, and the vibe after the opening set was a far cry from the restrained atmosphere traditionally associated with Centre Court, feeling much more like the Olympic atmosphere in 2012 when Andy Murray rode the wave to the gold medal on these grounds.

"I've never seen them so vocal," Williams said. "I've never heard boos here, so that was new for me. Hey, I've been through it all."

So it must seem, and now she is back to facing her sister. It will be their first match in any tournament since Venus Williams beat Serena Williams in three sets in the semifinals of the Rogers Cup in Montreal in August and only their third match in the last six seasons.

"She's in better form than I am, so I think she has a little bit of an advantage going into that match," Serena Williams said in an interview with the BBC immediately after her victory against Watson. "But at least one of us will be in the quarterfinal, so it will be good."

For about an hour, it seemed that both Williams sisters would advance to the fourth round with little trouble, but that was before Watson broke Serena Williams at 4-4 in the second set and then held her own serve to even the match at a set apiece.

She then twice broke Williams' serve, widely considered the biggest weapon in the women's game, to take a 3-0 lead and had points on her own serve to go up 4-0.

"She should have won the match at this point," Williams said. "She was up two breaks and playing really well."

But threatening Williams and defeating Williams remain two very different psychological propositions, as she has proved throughout her long, remarkable career, especially in 2015.

She twice had to rally from a set down in her run to the Australian Open title in January. She had to rally four times from a set down in her more agonizing run to the French Open title last month. But even after Williams won the first set against Watson, Friday's match turned into a thriller.

Williams has had more trouble than success in the last three Wimbledons, losing to Sabine Lisicki in the fourth round in 2013 and to Alize Cornet in the third round last year. But she avoided the upset this time by getting back to 5-5 in the third set with a deep return that Watson struck into the net with her backhand.

Williams held serve at love - an unusual development in this tight and emotional match. And Watson then saved two match points on her own serve before Williams, shrieking and gesticulating, managed to close out. She looked much more relieved than triumphant as she walked slowly to the net to shake hands with a young opponent who had very nearly become a big part of Wimbledon history, and who had very nearly put a family affair on hold.