The American, 37, will play the Spaniard in the Wimbledon final after both were dominant in straight sets wins on Thursday. For Williams, it's a first Wimbledon final since 2009, while Muguruza fell at the last in 2015.
A brilliant display of controlled hitting handed Williams a 6-4, 6-2 win over home favorite Johanna Konta and ensured she'll became the oldest Wimbledon finalist for 23 years when she meets Muguruza on Saturday.
Twenty years after making her debut at the tournament, the older of the Williams sisters is in to her ninth final, and will be confident of adding a sixth title nine years after her maiden win in 2008.
Konta initially kept pace with her American opponent but Williams drew on all her experience to break in the tenth game and undo all the Brit's good work until that point.
The crowd on Centre Court fell silent and Konta seemed to be equally muted in her response to Williams, struggling to make any impact in the second set.
Fittingly, Williams finished proceedings with a booming forehand that was typical of the power that got her over the line. She found time to lament the absence of her sister Serena, who is pregnant and taking time away from the game.
"I couldn’t have asked for more but I’ll ask for more," she said. "I know [the crowd] love Jo and she gave it her all today. I think my experience helped a lot. I’m just so happy. I miss Serena terribly. I wish she could do this for me."
Muguruza powers her way to final
Williams will play Muguruza after the number 14 seed, who has lost two of the past three Wimbledon finals, cruised past 87th-ranked Rybarikova 6-1, 6-1 to progress earlier in the day.
The 2016 French Open winner, seeded 14th, took a 3-0 lead in just ten minutes thanks to an aggressive approach. The 23-year-old preyed on her opponent's apparent nervousness and managed to make the game look easy. Magdalena Rybarikova, from Slovakia, was the lowest ranked Wimbledon semifinalist in nine years.
"I played very well, for sure" said Muguruza, who previously beaten Germany's Angelique Kerber in the last 16. "I'm going to enjoy it. Being in a grand slam final is a great achievement."
The final will be held on Wimbledon's Centre Court on July 13.
AFP, AP (ft/mp)