City can move six points clear of the Gunners if they win at the Emirates on Saturday Night Football, and they still have two games in hand over all their top-four rivals.
City have had another superb week, thrashing Fulham before an emphatic win over rivals Manchester United at Old Trafford on Tuesday, and they are the Sky Bet favourites to clinch a second Premier League title this season.
But Pellegrini said on Friday: "It is not the last match and not the match that will decide the title.
"Of course it is a big game - it is against a team that is also fighting for the title - but it is a matter of six points, which would be a very important difference.
"If we win on Saturday and win our two games in hand then we can be 12 points on top of Arsenal - that is also a very important difference. A win would be a huge step to continue the way we have been going so far."
Pellegrini has also insisted he is not under any more pressure than other managers to deliver the championship for City's billionaire owners.
"All the big teams must always be under pressure to win titles. It doesn't matter if they have won one before. The ambition has to be to win as much as you can every year for every big team," the Chilean added.
"We never talked with the owners that we must win this title. They do not ask about this title, they ask about the way the team is playing, and that way I hope we can win titles. "
Arsenal v Manchester City is live on Sky Sports 1HD from 5pm on Saturday Night Football.