Williams was not helped by a jarred Achilles injury early in the deciding set that required heavy strapping and her quest to equal Margaret Court's record of 24 Grand Slam singles titles goes on.
Instead, it is two-time Australian Open champion Azarenka who will face Naomi Osaka in a quite remarkable story of resurgence.
The 31-year-old had been a shadow of her former self since her stop-start return from maternity leave in 2017 and had almost been written off as a major contender prior to her victory on the same courts in the Western & Southern Open last month.
"I knew it wasn't over at 5-3," said the Belarusian. "I've been there before. Today was going to be different. I was young, my ego was way too big. Now it's a little smaller and the result's coming."
