Race officials found that the Brazilian's car used during the first half of the 43-lap contest -- in Formula E, all drivers use two cars per race -- was found to be 1.8 kilograms under the minimum weight of 888 kg
The Brazilian who drives for the German-based ABT Schaeffler team -- one of nine teams competing in this the second season of the all-electric race series -- was presented to the crowd at the Autodromo Hermanos Rodriguez circuit as the winner during the podium ceremony only to be disqualified a short time later.
D'Ambrosio, who drives for the American team, Dragon Racing, had started Saturday's ePrix on pole and led during the first half of the race but was overhauled by di Grassi shortly after the drivers pitted to complete a mandatory switch of cars
midway through the race.
Di Grassi made the most of his Fan Boost -- a online poll where the three most popular drivers are awarded a temporary speed boost -- to overtake D'Ambrosio and quickly built up a comfortable lead and eventually crossed the finish line five seconds clear of the Belgian with championship leader Sebastien Buemi a close third.
Renault e.Dams driver Buemi and D'Ambrosio were engaged in a fierce battle for what was retrospectively first place in the latter stages of the race.
At the start of lap 29 of the 43-lap race, Buemi plowed into the back of D'Ambrosio's car, leading to both drivers exchanging heated words with their respective pit crews via team radio.
The pair were wheel-to-wheel again six laps later with Buemi managing to pass D'Ambrosio, but only by illegally cutting the chicane at the end of the pit straight.
Di Grassi's disqualification has enabled Buemi to extend his lead at the top of the drivers' championship from four points to 22.
If the original result had stood, di Grassi would now be leading the drivers' championship by six points from the Swiss but now finds himself with 76 points compared to Buemi's 98.
The result moves D'Ambrosio up to fourth place with 58 points, two points behind Britain's Sam Bird.
The DS Virgin Racing driver couldn't repeat the heroics of the previous round where he sealed a thrilling win in Buenos Aires
-- this time he had to settle for a creditable sixth place.
Reigning world champion Nelson Piquet Jr. continued his lackluster title defense.
The former F1 driver who races for the China-based team NEXTEV TCR crashed during qualifying before he'd been able to set a lap time. He was unhurt but started the race from the back of the grid and eventually finished in 13th.
Next up, the all-electric race series travels to Long Beach, California at the end of March before Formula E heads to Europe for the final five stages of the season.