He said: "The crowd was a bit of a disappointment because we were playing a big team.
"Maybe there were few people in because the game was on television and it was a cold night.
"But hopefully if we get a home draw in the next round then the fans will come back in numbers."
"It was a good performance and a great victory. Every win increases our confidence and this was a big win.
"The goal came because of the work we had done in training and it was a brilliant cross from Ricardo.
"We are now looking forward to the draw and the next round of the cup. We will try our best again."
Meanwhile, Spanish midfielder Ivan Campo has been ruled out for several weeks with a broken foot.
It is the second time the player has suffered a broken foot this season and poses a serious selection headache for Allardyce, who is without a host of key players ahead of a busy schedule.