The Reds beat City 3-1 at home on Sunday to solidify their top position in the Premier League.
While the reigning champions are now nine points behind Liverpool, Robertson respects the kind of run they could go on later in the season.
"Massive for us. A big game against our closest rivals from last year," Robertson told Liverpool's official website of the win over City.
"Both of us were in a league of their own last year and it looks as if there's going to be a couple of others sniffing about this year. But I still believe if you finish above Man City then I think you'll get the title.
"It's a massive win for us and it's just another one that we've got to tick off. There's still a long, long way to go, but it's always nice to beat your rivals."