Dutchwoman Kiki Bertens takes on German 13th seed Julia Goerges in the final quarter-final.
On No. 1 Court, 2017 French Open champion Jelena Ostapenko is in action against Dominika Cibulkova, who is playing her third Wimbledon quarterfinal.
The Italian's comments ahead of the match that she does not follow tennis will have raised eyebrows but, competing in her first Grand Slam quarter-final, she troubled Williams significantly with her movement and power and took the first set.
German 11th seed Angelique Kerber reached the Wimbledon semi-finals with a 6-3 7-5 win over Russian Daria Kasatkina on Tuesday but needed seven match points to see off the 14th seed.
Rebounding from her shock first-round elimination in her Roland Garros title defence, Ostapenko has marched through the Wimbledon draw without dropping a set.
"I didn't quite take my chances in the first set but tried to stay calm and keep working for the points", added Goerges.
"Even when I was down the first set, I thought, "well, she's playing great, I'm doing a lot of the right things".
CONTENTIOUSLY dumped from Wimbledon's seedings, Dominika Cibulkova has charged into the quarter-finals - only to be accused of poor sportsmanship.
From those appearances, she has reached three finals, all in 2016, when she beat Williams to win the Australian Open, lost to her in the Wimbledon final, then won the US Open.
Ostapenko, 21, was certainly in step on Court One as she blasted a stunning 32 winners.
She quickly worked out a way to hurt the 23-time grand slam champion and it was not just her clothes that were eye-catching as some impressive serving and a barrage of cross-court forehands saw her dominate.
"To be honest, I am not feeling the pressure because I am not looking who is left or not from the seeds". "I was just trying to enjoy it because its really great to be here in the second week and now I'm in the semis and really happy with the way I played. It was too hard so I had to ice it", Ostapenko said.
The young Latvian has been her fiery self so far this Wimbledon, and has been particularly ruthless on return, winning 20 of 38 return games on her opponents' serve.
"I feel like I am back, I still have a long way to where I was".
"I had no sympathy because it's just about the chair umpire".
The German, who was runner-up to Serena Williams two years ago, triumphed 6-3 6-3 on Centre Court and is now one win away from a third grand slam title.
Ostapenko came out on the offensive, converting her sixth break point to take an early lead, but she was immediately pegged back by the Slovak who broke to love before securing the first hold of the match. By the time she flubbed a backhand while falling behind 5-1 in the second, she dropped her racket and screamed.