Serena Williams admitted she had to fight all the way to overcome Alison Riske and move a step closer to an eighth Wimbledon title.
A thrilling 6-4 4-6 6-3 victory in the all-American showdown on Centre Court ensured the 37-year-old reached her 12th semi-final in 19 appearances at the Championships.
Riske, unseeded and ranked 55, had knocked out world number one Ashleigh Barty 24 hours earlier, and she pushed Williams all the way.
Serena comes through an almighty test... Winning a hard-fought quarter-final against compatriot Alison Riske, @serenawilliams reaches her 12th #Wimbledon singles semi-final pic.twitter.com/UYHmxO0nuP — Wimbledon (@Wimbledon) July 9, 2019
But for Riske there was no reward despite five breaks of serve – converting every single break point she created – against the 23-time grand-slam winner.
"I just needed to just fight," admitted Williams.
"Alison, I mean, she played great throughout the whole tournament. She's beaten so many amazing players, players that have had great years.
"She was not giving it to me. I needed to step up and take it. That's what I had to do."
Having been pegged back to 1-1 by the stubborn Riske, Williams seemed to find a second wind after tying her hair up.
"It was just in my way. I was missing a shot because it was in my face," she said.
"I was like, 'this is not happening'. I just needed to get it out of the way, put the business bun up and just get to business."
Breaks were exchanged again twice at the start of the decider, the Americans matching each other blow for blow until a stunning Williams volley and a Riske double-fault broke the 29-year-old once more.
Serving for the match after two hours and one minute, Williams fired a 19th ace down the middle to seal her place in the last four.
It was her toughest test yet, and proved that despite an injury-hit year, Williams has lost none of her physical strength.
"I just threw my racket. I got fined," she said.
Asked how much damage she had actually done, Williams replied "I mean, I guess if you could tell me, I would appreciate it.
"I have always been an Avenger in my heart. Maybe I'm super strong, I don't know."
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