Tomas Berdych has become the latest seeded player to crash out of the Stuttgart Open, with Spaniard Feliciano Lopez edging past the Czech in three sets to reach the last four.
And, around 340 miles away at the Ricoh Open in Rosmalen, 20-year-old Alexander - who is more than nine years younger than Mischa - lost 7-6 (7-5) 6-2 to Luxembourg's Gilles Muller.
Benneteau failed to work a single break point against the promising star, who produced an utterly dominant display to set up a clash with Gilles Muller, a 6-3 3-6 6-4 victor against Aljaz Bedene.
Zverev double faulted on match point to end it.
Feliciano Lopez beats Mischa Zverev to book place in Stuttgart final
The experienced Lopez had earlier edged out German Mischa Zverev in the first semi-final, 6-7 (2/7), 7-6 (7/4), 7-5.
The 35-year-old Lopez, who last made a final in August 2016, reached his fourth career grasscourt final as he prepares for Wimbledon and will face fourth seed Frenchman Lucas Pouille on Sunday.
Sixth seed Zverev hit 16 aces and looked comfortable throughout.
Pouille's semifinal opponent will be another Frenchman, Benoit Paire, who ousted Jerzy Janowicz of Poland 6-1, 7-6 (4).