"Given all the changes it's no surprise that it wasn't a fluid performance. It was a fluke goal but with extra time looming large I was very happy to see it go in," Coppell told the club's official website after the 1-0 win.
"Luton are a good, strong, aggressive side and I fully anticipate them being near the top of the league at the end of the season, they are hard to play against and hard to beat.
"Beyond this round all of a sudden you start to see more of an edge to the competition. If we get a big game in the next round, this will become a great tie to win."