With Lucas back in the holding midfield role, the Reds dominated throughout and Allen believes everyone in Brendan Rodgers' side benefited from his presence.
"You're always going to miss quality players like Lucas and it's great to have him back in the side," Allen told the Liverpool Echo. "When he pulled up injured in the Man City game it was a bitter blow.
"He had worked so hard to get back from the knee injury. It was a disappointing setback on a personal level but also from the football club's point of view.
"His return, with the steel and quality he brings, is only going to help the team going forward.
"It's a very important role. If you look at the top teams, they all utilise that position and have a quality player there.
"Lucas is vital for the way we play.
"With him back playing, I'm sure we'll get the benefits of that in terms of points and our position in the table."