The Baggies came from behind to score twice in a span of two minutes during the second half to seal a spot in the fourth round of the competition.
The Baggies assistant boss admitted that the line-up fielded by the home side was one that anticipated City boss Roberto Mancini making changes to his team, which he did to give some of his fringe players a run out on the pitch.
"It was a great result," Appleton told reporters. "Really positive. Made numerous changes and the lads responded well," said Appleton.
"We were second guessing their side bearing in mind they have Chelsea on Saturday but there was still a lot of experience in the side.
"They brought the cavalry on at the end and we were under the cosh for the last 15 minutes but we did enough to win."
Our provides the best breaking news online and our football fan community is unmatched worldwide. Never miss a thing again!