Simon was defeated by Pablo Andujar 6-4, 7-5. Andujar won six of Simon's seven break-point chances in holding him off. He finished with three points himself.
Monfils finished quarterfinal play with a 6-2, 6-3 win over Robin Haase. He dropped his serve once while winning nearly 70 percent of the points on serve. He won more points (31-30) than Haase did when Haase served.
Also Thursday, Albert Montanes defeated Paul-Henri Mathieu 6-4, 6-1 without losing his serve and Edouard Roger-Vasselin outlasted third-seeded Sam Querrey 3-6, 7-6 (7-2), 6-1. Roger-Vasselin lost nine points -- saving three break points -- on serve in the final set.
Monfils will go against Andujar in one of Friday's semifinals. Monfils has won both previous meetings. Roger-Vasselin earlier this year took a three-set decision over Montanes in their only match.