The Abt Schaeffler all-electric car raced by the Brazilian in his first stint was found to be 1.8kg under the mandatory minimum weight of 888kg, in breach of Article 5.1 of the FIA Formula E technical regulations.
This means pole sitter D’Ambrosio earned his second victory in the series - and incidentally, the Belgian’s maiden FE success also came after a Di Grassi exclusion in Berlin last year.
Promoted to second was Renault e.dams’ Sebastien Buemi, who thus reclaimed the points lead he briefly lost to Di Grassi.
Formula E Mexico: Race highlights
D’Ambrosio’s Dragon Racing team-mate Loic Duval would have been third but for a 15-second penalty that he was handed post-race for not respecting track limits.
That left Nicolas Prost third instead of fifth as he joined team-mate Buemi in the Mexico ePrix top three.
The Frenchman was also credited with the fastest lap of the race after D’Ambrosio was stripped off the honour.
The slew of post-race penalties means Buemi leaves Mexico with a 22-points edge over Di Grassi in the Drivers’ championship.