Laurent Robert got the other goal as Newcastle beat Southampton 3-0 away.
Dyer underwent a bowel operation on Monday after missing two games with a stomach problem caused by constipation.
"Kieron trained very gingerly on Tuesday, was a bit better on Wednesday,trained lightly on Friday and then played like that," said Robson.
"He was quite remarkable and finished the match with a sensational goal.
"It was an exquisite finish. I always say to him `Can you finish?' Today he said 'yes'.
"We used him up front, and he made a difference to the side.
"What I like about Kieron is he harries and hassles people. His work off the ball is just as good as on the ball."
Robson, speaking about his players response to Freddy Shepherd's criticism, added: "The players have given a magnificent response in the only way they can - and that's by showing their footballing ability.
"We've lost two games in 14 and kept our calm and were professional about it.
"We're in the fourth round, which is where we very much want to be."
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