Simon, who is a two-time winner of the Metz tournament, took an early lead in the first set but failed to convert the break as Gasquet broke in the 10th game to level the set. Gasquet won the first two points in the tie-breaker before Simon fought back to win the set in just under an hour.
This was Simon’s first ever win over Gasquet. He now faces Radu Albot in the last four. “It is very, very hard to win against a player you have never beaten, but I started well,” Simon said.
Nishkori had a tougher quarterfinal match as he needed three sets to defeat Nikoloz Basilashvili.
Wawrinka in St. Petersburg semis
Stan Wawrinka beat Damir Dzumhur in straight sets to reach the Saint Petersburg Open semi-finals.
The 33-year-old Swiss beat the defending champion 6-3, 6-4 in one hour and 11 minutes. In the last four, Wawrinka will face Martin Klizan, the 2012 champion, who fought back from a set down to beat Denis Shapovalov.
Top seed Dominic Thiem also entered the semis after edging Daniil Medvedev 6-2, 3-6, 7-6 (7/2) in three sets.
In the semis, Thiem faces fifth seed Roberto Bautista Agut, who beat Marco Cecchinato 7-6 (7/0), 6-3.