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The third seed, Zverev produced 15 winners and nine unforced errors, compared to 12 and 25, respectively, for Humbert.
Djokovic avenged his US Open final defeat with a 4-6, 6-3, 6-3 victory.
Khachanov will now play his first Masters 1000 final on Sunday against the winner of the blockbuster second semi between Novak Djokovic and Roger Federer.
The top seed was handed an opening night fright by his good friend Feliciano Lopez, but rallied to beat his fellow Spaniard 4-6, 7-6(5), 6-4 .
Nadal beat fellow Spaniard Pablo Carreno Busta 4-6, 7-5, 6-1, a result that gave Argentine Diego Schwartzman the last spot at the season-ending ATP Tour Finals.
The top seed was forced to save a set point before overcoming Australian Jordan Thompson 6-1, 7-6(3).
Zverev will look to claim his fourth Masters title against Russian third seed Daniil Medvedev, who scored a commanding 6-4, 7-6(4) victory against Canadian Milos Raonic.
The third seed, who also defeated Zverev in the Shanghai final last year, clinched his first title of the year.
Results 1-8
