McArthur said: "This was a massive game for us - we need to win at home and take as many points as we can.
"In some ways, the cup gives you a rest from the SPL, but I would like to carry on in the league because we've been doing well recently.
"We knew that this stage of the season was the start of a run of games where we could try to take a lot of points.
"We've beaten Kilmarnock, Motherwell and now Aberdeen, who are a good side, and we need to continue that; hopefully we'll start getting wins to take ourselves away from the bottom of the table but it's going to be hard in our first year in the top flight.
"The difference recently is that we've started to learn how to play in this league and we've adapted."