Monaco rallied to defeat No. 5 seed Albert Montanes 3-6, 6-1, 6-1 and Chela survived a 3-hour match to down Joao Souza 5-7, 7-6 (8-6), 6-1.
Monaco's win over Montanes was his first in their three meetings.
The other quarterfinals saw seventh-seeded Carlos Berlocq defeat qualifier Federico Delbonis 6-3, 6-4 and Jeremy Chardy oust Frederico Gil 6-2, 7-6 (7-5).
It will be Monaco taking on Chardy and Chela facing Berlocq in the semifinals of this, the first clay-court tournament of the year on the ATP Tour.