Venus Williams upset little sister Serena 6-7(2) 6-2 6-3 on Saturday to register the first win over her top ranked sibling in five years and move into the finals of Rogers Cup in Montreal.
The meeting marked the 25th time the illustrious tennis siblings had squared off but the first time Venus had come out on top since a 2009 semi-finals encounter in Dubai.
Despite the loss, world number one and defending champion Serena holds a 14-11 edge in their head-to-head showdowns after coming out on top in their previous five encounters, including the 2009 Wimbledon final.
But the clashes, which at one time were an almost regular and welcomed occurrence on tennis courts across the globe, have become rarer-and-rarer with their meeting in Montreal just the second since the 2009 Tour championships.
"It was a tough match out there," said Venus, who will now await the winner of the other semi-final between third seeded Agnieszka Radwanska of Poland and Russian Ekaterina Makarova. "I don't think we played for a number of years, as well. It's not like we've been playing year in and year out.
"I definitely expected a tough match. She played well. She hit so many aces.
"What's so unique about the situation is that we're both very good players.
"I think typically you may have some siblings, one is quite good, one is not as good, so you kind of know what the result is, or the one that's better knows they're going to win.
"I think we both know when we walk out there, it's not like you're guaranteed a win. I think that's what makes it challenging for both of us."
While a Williams-Williams matchup is one tennis fans have always looked forward to, for the sisters it is something they could live without.
There was little excitement when the match was decided, the two players walking slowly to the net and hugging briefly.
Venus' reaction at ending her sister's Rogers Cup title defense was muted as she turned and offered a small wave to the crowd before slumping into her courtside chair and staring blankly across the court.
While the Williams are about as close as sisters can be, on the court there is no love lost between the two siblings, who between them have won 106 WTA Tour singles titles, including 24grand slams.
Then the goal is always the same — win.
"For me it was just a regular match," shrugged Serena. "Obviously she's my sister but I still want to go out there and try to play well and try to win.
I think Venus played a great match. It was what it was.
"Obviously I always want her to do the best that she can. I want to do the best that I can, too.I just got to do better, that's all."