For his fourth participation after 2015, 2016 and 2017, Muguruza has reached this stage of the competition for the first time.
She is the second in her country to achieve this, after Arantxa Sanchez who bowed to Steffi Graff in 1993, at Madison Square Garden in New York.
For their first confrontation, she was the most solid in the exchanges, returning with her game against the powerful shots of Badosa, who managed too few winners.
The winner of Roland-Garros in 2016 and Wimbledon in 2017 was able to break in the first set to lead 3-1, before keeping her throw-in and concluding on her first opportunity, still on opposing service.
The start of the second set was closer, Badosa being more aggressive, with notably good shots along the lines.
But she fell for her first serve against the opposite wall.
Muguruza, who had just broken his fourth opportunity after eight minutes of exchanges, was still the most effective in the next game, long to emerge too, to consolidate his lead to 3-0.
Her 24-year-old rival, who owed her first participation in the Masters to her surprise victory at the Indian Wells tournament in October, dropped slightly, to lose in 1h25 min.
Muguruza, who Mexico succeeds in having won the Monterrey tournament twice, is now waiting to see who she will face in the final on Wednesday.
It will be the Estonian Anett Kontaveit (N.8) or the Greek Maria Sakkari (N.4), opposed in the evening.
© 2021 AFP