Serena and Venus Williams are one win away from clashing in the Wimbledon final for an incredible fifth time.
Top-ranked Serena stepped up her title defence with a steely-eyed 6-4 6-4 quarter-final win over Anastasia Pavlyuchenkova after Venus advanced to the last four at the All England Club for the first time in seven years with a 7-6 (7-5) 6-2 defeat of Yaroslava Shvedova.
Serena finished off Pavlyuchenkova with her eighth ace after just 73 minutes and next faces another Russian in the unseeded Elina Vesnina, who ousted Slovakian 19th seed Dominika Cibulkova 6-2 6-2.
Continuing her extraordinary tennis renaissance, 36-year-old Venus is the oldest player to reach the Wimbledon last four since Martina Navratilova in 1994.
Sixteen years after winning her first of five crowns on London's hallowed grass courts, and five years after being diagnosed with Sjogren's syndrome, Venus will play Australian Open champion Angelique Kerber on Thursday for a place in Saturday's title match.
"We're just happy to be in the semi-finals. It's so cool, it's just great," Serena said. "If I'm not in the final, obviously I want her to win so bad."
Champion in 2000, 2001, 2005, 2007 and 2008, eighth-seeded Venus will be contesting her 20th grand slam semi-final as she continues her pursuit of an improbable eighth major singles title.
The former world No.1 has won all eight previous semi-finals at Wimbledon, including the 2000 decider when she defeated 18-year-old Serena en route to her first title at SW19.
"Semi-finals feels good," Venus said. "But it doesn't feel foreign at all, let's put it that way."
Despite her impeccable credentials, Venus will be up against an inspired opponent.
After taking 30 slams to land her breakthrough in Merlbourne, Kerber is now eyeing a second in six months after denying Romanian fifth seed Simona Halep 7-5 7-6 (7-2) in a rollercoaster encounter earlier on Tuesday that featured 13 breaks in 24 service games.
"I'm really happy that I won this because it was so close. I won the last point and that's what counts," Kerber said.
At 29, Kerber - a semi-finalist in 2012 too - believes she is playing the finest grasscourt tennis of her career. She is the only woman not to have dropped a set yet in five matches this campaign.
"I'm trying to focus on my game, being aggressive and moving well," Kerber said.
"I've had a great year so far with the Australian Open title and I'm feeling so good."
With her victory, Serena also closed to within two wins of a seventh Wimbledon crown - and record-equalling 22nd grand slam title to match Steffi Graf's open-era benchmark tally.
"I'm excited to be able to win that one and get through and I felt really good," she said.
"I knew I had a really tough opponent today."