"I said to them you might not be the best players but you must be the best squad in terms of team spirit, of collaboration and in commitment," Riga told the club's official website.
"Then you can make it through as a team, not alone and that's exactly what they did."
Riga took over from Chris Powell almost two months ago and has guided the South London club to six wins and three draws in 15 matches to guarantee their Championship status.
Despite his impressive managerial display, the Belgian hinted that his only job was the "short mission" of staying up.
"I'll enjoy the moment," he added. "I'm very proud to have this success in this short mission and for the future, we will see."
Riga took over with Charlton dead last in the division.