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Gillingham had defenders John Hills and Ian Cox sent off as they suffered a 12th League defeat of the season in losing at Derby on Saturday.
They were reduced to 10-men in the 34th minute when Hills was ordered off for a second yellow card after holding back Manel.
They were down to nine-men in the 78th minute when Cox was dismissed for a second caution following a foul on Marco Reich.
Player-manager Andy Hessenthaler afterwards refused to comment on the performance on Cambridge referee Kevin Wright.
Derby, who had won five of their last 20 games at Pride Park, took the lead in the 13th minute when debut-making Jamie Vincent curled in a free kick that cannoned in off the far post.
They increased their lead in the 61st minute when another debut-maker,Rob Edwards,found the net with a deflected drive.
Former Derby favourite Tommy Johnson scored the goal of the game with a stunning 69th minute left-footed drive but Derby's numerical superiority made sure they took maximum points.
Gillingham will take heart from Patrick Agyemang's debut as he went close to scoring in the first half when he forced Derby goalkeeper Lee Grant into several outstanding saves.
Gillingham confirmed after the match that they had signed Grimsby midfielder Alan Pouton for what is thought to be a £45,000 fee.
He will be available for next Saturday's FA Cup tie at Burnley.
Attendance: 20,473