Venus and Serena Williams both won twice on Friday to set-up a family affair in the semi-final of the aptly-named Family Circle Cup in Charleston.
They will now go head-to-head for the first time in over three years - as the last meeting of the American superstar sisters was in the final of the season-ending WTA Championships in 2009 when Serena beat Venus.
Serena, the younger sister who leads their career series 13-10, saw off American qualifier Mallory Burdette 6-4 6-2 before knocking out Czech sixth seed Lucie Safarova 6-4 6-1 to make the all-Williams clash happen.
Venus had already clinched her place in the final four, at the expense of two fellow Americans, first knocking out Varvara Lepchenko 6-2 4-6 6-2 and then earning a 6-4 6-4 victory over Madison Keys in the quarter-finals.
Serena is defending her title this week and, as world number one, heads into the semi-final against 24th-ranked Venus as favourite.
"It was really motivating to see Venus win today. I figured if she can win two matches, I have no excuse not to win my two matches," Serena Williams said, according to the WTA website.
Now 31-year-old Serena is relishing the battle against her 32-year-old sister.
"Venus is the toughest opponent I've ever played. I think she's beaten me the most out of any player. I know her game and she knows my game," Serena said. "I think it'll be a great match tomorrow."
Jelena Jankovic ended the run of qualifier Eugenie Bouchard, with the Serbian posting a 6-2 6-1 victory over her Canadian opponent.