The £3.5m striker had been an unused substitute in the previous four Premier League matches but he provided a spark for the Rams as they searched for an equaliser against Reading.
He went close late on and his brief contribution, along with that of fellow-subs Giles Barnes and Eddie Lewis, pleased manager Billy Davies.
"I thought they performed very well," said Davies after the 1-0 defeat.
"They were lively and positive, showed the energy we needed and Rob did add something. He nearly scored a wonderful goal, which he is capable of doing.
"He will come good once we get him in the right partnerships and get the balances right."