Monfils also reached the quarterfinals last week in Metz, his first tournament since May after being sidelined by a right knee injury.
The Frenchman used five breaks of serve to trump the three he lost, beating Troicki a third straight time. Monfils will meet 2009 champion Gilles Simon, who defeated Go Soeda of Japan 6-4, 6-4.
Fernando Verdasco of Spain edged Donald Young of the U.S. 7-5, 6-4, and Bernard Tomic of Australia reached his first quarterfinal since April, rallying past Dudi Sela of Israel 4-6, 6-3, 6-4.
Also, third-seeded Milos Raonic of Canada beat Ivo Karlovic of Croatia 7-6 (3), 6-4 in the first matchup of big servers. Raonic had 14 aces to nine for Karlovic, and converted his only break point chance.
"I was a bit hesitant in the first set, and tried to figured out (the indoor court) in the second,'' said Raonic, who will face Jarkko Nieminen of Finland.