Derby's new signings helped the Rams register a crucial win but Gillingham were left fuming by the sendings off of John Hills and Ian Cox.
Jamie Vincent marked his debut with a free-kick that put Derby in front and Marco Reich impressed with his pace and movement on the left.
But Gillingham were far from happy with the performance of referee Kevin Wright and could ask the Cambridgeshire official to review the two red cards.
Both Hills and Cox walked for second yellow cards but even Derby boss George Burley though the sending off of Hills was harsh.
But there was no questioning the impact Vincent and Reich had on the game as they gave struggling Derby a new look that has been missing for most of the season.
Vincent curled a left-foot free-kick just inside Gillingham's right-hand post in the 13th minute and Reich was also close to finding the target as Derby played some of their best football of the season.
But it still needed inspired saves from Lee Grant to deny Patrick Agyemang and former Rams star Tommy Johnson was also foiled by the England Under-21 keeper.
A second goal by Rob Edwards eased Derby's nerves when his low shot from 20 yards was deflected past Nico Vaesen but Johnson put Gillingham back in the game with a scorching shot from 25 yards.
Cox departed 11 minutes from time for a second booking in the space of three minutes but although Gillingham were down to nine men, they really pushed Derby in the closing minutes.
It needed a desperate clearance from Grant to stop Agyemang breaking through but Derby held on for a win that lifts their hopes of staying in division one.
But striker Lee Morris who was left out of this game, could re-join Sheffield United next week if the clubs can finally agree a fee.