The top-ranked Williams fought back from a set down Tuesday to beat Azarenka 3-6, 6-2, 6-3 on Centre Court to reach the Wimbledon semifinals and keep her bid alive for a fourth straight major title -- a "Serena Slam."
Williams is two wins away from winning her fourth consecutive major tournament, which would match the non-calendar Slam she last achieved in 2002-03. A victory in the US Open would then be left to complete a true Grand Slam, which hasn't been accomplished since Steffi Graf won all four in the same year in 1988.
Coming up with big serves when she needed them and getting stronger as the match wore on, Williams put on a dominant performance in the final two sets, winning seven straight games at one stretch, to run her Grand Slam winning streak to 26 matches.
"It's been up and down, up and down, but somehow I'm still alive," Williams said. "I don't know how. I'm just happy to be still here."
Williams hit 17 aces, including three in each of her final two service games, to extend her career record against Azarenka to 17-3 -- including 10-0 in Grand Slam play.
"We just saw today why Serena is No. 1,'' said Azarenka, a former No. 1 herself and two-time Australian Open champion. "I haven't seen her play like this, honestly, even the last matches before that.''
Added Williams: "It was really fun out there. I found myself smiling at one point, and I saw Victoria smiling as well. It's such a great atmosphere to be out here and playing and doing the best that we can. I think we both really enjoyed it."
Azarenka, though, was less pleased after the match when asked about grunting from both players that drew laughs from some in the crowd.
"You know, I'm so tired of these questions all the time," she said. "It's so in a way annoying because guys grunt. I was practicing next to (Rafael) Nadal, and he grunts louder than me, and nobody notice that. Why? I don't understand why. Because the women on the court both trying their hardest and giving everything they have, and they make a noise. Is that a problem of tennis? It happens in every sport.
"So I think maybe it's time to just put it aside and not talk about it all the time because this is not what is important when there are two players playing on the Centre Court."
It's the first time Williams has reached the Wimbledon semifinals since 2012, when she won the last of her five titles at the All England Club.
Williams will next face Maria Sharapova on Thursday in the semifinals. Williams beat Sharapova, the 2004 Wimbledon champion, in this year's Australian Open final. Williams holds a career 17-2 advantage against the Russian, including 16 wins in a row.
"We haven't played each other at Wimbledon in a while but I look forward to it," Williams said. " I just really don't have anything to lose."
Sharapova looked ahead to another late-round showdown with Williams.
"Definitely no secrets between each other's games,'' she said. "That would be an incredible moment for me to step out on Centre Court against her again.''
The Associated Press contributed to this report.