Of all the scenarios Serena Williams could have envisioned for lifting her 22nd Grand Slam title and equaling Steffi Graf’s Open-Era record, her sister Venus being on the other side of the net, rather than cheering her on from her supporters’ box, surely wasn’t one of them. That prospect is now, though, a very real possibility.

Serena, who has suffered painful disappointment in the last three Grand Slams as she chases No. 22, has taken her expected place in the Wimbledon semifinals, where she will be a big favorite against Elena Vesnina. Now 34, Serena’s continued position at the top of the women’s game is remarkable. Yet her older sister has upstaged her so far at SW19.

At the age of 36, Venus Williams has become the oldest Grand Slam semifinalist since the great Martina Navratilova finished runner-up at Wimbledon in 1994. Williams dropped out of the world’s top 100 five years ago after being diagnosed with the autoimmune disease Sjogren’s syndrome. But, at an age when the vast majority of players have long since retired, Williams is now back in the top 10 and back in her first major semifinal since 2010.

“The road was six years,” Venus said after beating Yaroslava Shvedova in straight sets in the quarterfinals. “They go by fast thankfully. But I've been blessed, been really blessed, to have an opportunity to be here, have had an opportunity in the past to do this. I don't have any regrets about anything that's taken place in between. It's been a journey, but it' something that I’ve had to do and it’s made me stronger.”

She could now be set for another, most unexpected, chapter in the on-court rivalry between tennis’ most famous ever siblings. Remarkably, it would be the pair’s seventh meeting on the grass at Wimbledon, and fifth final. It is Serena who has had the upper hand, winning three of the sisters’ finals as well as their most recent meeting in London, in the fourth round last year.

A 28th career meeting between the pair on Saturday is not a foregone conclusion, however. While Serena will be heavily favored against Vesnina, who had never previously been to a Grand Slam quarterfinal never mind a semifinal, Venus will be going up against Australian Open champion Angelique Kerber.

The German beat Serena to claim her first Grand Slam title in Melbourne and could even finish Wimbledon as the world No. 1, if she wins the title and Serena fails to make the final. Kerber is also the only player to have reached the semifinals without dropping a set.

Venus, though, has plenty of pedigree on grass, which has proven her favorite surface, winning the Wimbledon title five times. Only three women have won the tournament more in the Open Era. Unsurprisingly one of those is Serena, who last year won her sixth.

Victory on Saturday will equal Graf’s haul of seven. However, it is another number that Serena is really chasing. And after agonizing near misses at the U.S. Open, Australian Open and last month’s French Open, she is again looking primed to get to 22 Grand Slam titles. But now to get there she may not only have to cope with the pressure of not only going for history but doing so against her older sister in what would be the oldest Grand Slam final in the Open Era.

Before all that, though, the sisters will take to the Wimbledon courts on the same side of the net, looking to keep their hopes alive of lifting the women’s doubles crown.