Whoever wins will set the final to face either Ralf Nadal or Novak Djokovic.
The first semifinal at Centre Court, between No. 8 seed Kevin Anderson of South Africa and No. 9 John Isner of the USA, features two powerful servers with similar games who have a lot less star power and considerably fewer Grand Slam trophies, to say the least: The Nadal-Djokovic combined count is 29, including five at Wimbledon.
But back came Nadal to level before an enthralling final set which was punctuated by great shot-making and spectacular dives and falls by both players.
The victor will play either John Isner or Kevin Anderson in Sunday's final. He's one of the more complex players that I ever saw on our sport.
While Nadal and Djokovic are old hands at winning Slams, the man stood on the opposite side of the net in Sunday's final will be bidding to win a first major.
Nadal has 17 major titles, two at the All England Club.
They played each other at college - still the main nursery for professional tennis in the United States - and have met 11 times on the Tour.
Djokovic's 2017 Wimbledon campaign ended in a quarterfinal retirement with an elbow injury which led to surgery and precipitated a worrying dip in form and confidence.
"It's feels great to be in the last four of a slam", the 12-time major victor said.
That match spanned 11 hours and five minutes, with Isner eventually triumphing 70-68 in an astounding final set.
Isner double-faulted to set up a set point for Anderson when serving at 5-4, but he saved it with a 129 miles per hour second serve that the South African couldn't return. I remember chatting to Andy Murray before the tournament and we felt that...
Nadal advances to his first Wimbledon semifinal since 2011.
Besides playing for the Wimbledon title, there was plenty of financial incentive for both players.
Cape Town - South African-born Kevin Curren knows the challenges of Wimbledon better than most.
Anderson eliminated eight-time Wimbledon champion Roger Federer in the quarterfinals.
I think I played really good tennis today.