Loit recovered from 4-2 down in the first set to force a tie break which Mauresmo won 7-3. The former world number one managed the telling break in the ninth game of a tight second set before advancing to the last four in sluggish fashion.
Mauresmo, who slumped to a second round defeat in Rome last week, entered the tournament in order to get more competition before Roland Garros which starts on Sunday.
The Wimbledon champion, who has never made it past the quarter-finals of the French, has looked below par since returning to action earlier this month after two months out because of appendicitis.
Mauresmo will play either compatriot Marion Bartoli or Russia's Elena Vesnina for a place in Saturday's final.
Serbia's Jelena Jankovic, the second seed, will play Spaniard Anabel Medina Garrigues in the other semi-final.
(Writing by Patrick Vignal in Paris)
