The top-seeded Monfils beat fellow Frenchman Josselin Ouanna 6-4, 7-5, hitting 12 service aces, and the No. 2 Ferer was a 6-3, 6-4 winner over Sweden's Filip Prpic.
Elsewhere, seventh-seeded Yen-Hsun Lu of Taipei beat South Africa's Raven Klaasen 6-4, 7-5; while India's Somdev Devvarman beat Brazil's Thiago Alves 6-4, 6-1.
Friday's quarterfinal matches are Feliciano Lopez-Rajeev Ram; Stephane Robert-Dustin Brown; Monfils-Lu; and Ferer-Devvarman.
The eventual champion takes home a $75,700 winner's check.
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