Monfils came back last week from nearly four months out with a right knee injury and reached the semifinals in Metz in his French homeland. On Wednesday, he blew a 3-1 lead in the third set. Anderson went ahead 5-4, but Monfils won the last three games to move on.
"I didn't play big tennis, just good enough to win. That's the good thing,'' Monfils said. "I need more time to be good and confident.''
Go Soeda of Japan beat local wild card Danai Udomchoke 6-4, 7-5 for a fourth straight time, and Ivo Karlovic of Croatia defeated Marinko Matosevic of Australia 6-3 6-4.