The win lifted Valencia up to eighth place on 23 points.
They almost made the perfect start with a Feghouli's strike blocked by Keylor Navas in the opening minutes.
Piatti pounced on a loose ball to open the scoring before halftime and Feghouli's clinical finish wrapped up the points with less than 20 minutes remaining.
In the day's other matches Almeria downed Granada 3-0 while bottom club Real Betis held Real Valladolid to a 0-0 draw.
- Sports & Recreation
- Keylor Navas