People say I'm a bit harsh on Arsenal sometimes, but it's the same old story with them every year.
A couple of weeks ago they put in one of the best performances you're likely to see as they wiped the floor with Braga in the Champions League. Then 10 days later they got slaughtered at home by West Brom.
If you want to be league champions then things like that can't happen. They've been an inconsistent team for the last few years and it doesn't seem to be changing.
You can't put it down to youth because they're not the youngest team around any more. This is a team of internationals who have been together for a long time and have plenty of experience. They just don't seem to have the consistency to win the league.
They don't have a good enough goalkeeper to win the league either, but that's not Manuel Almunia's fault, it's the manager's fault.
They need a goalie, simple as that. If you go through history and look at any team that has won a title in England or around the world, they all have a top-drawer goalie.
Almunia is good, but he's not top-drawer. His mistakes against Liverpool and West Brom have cost Arsenal at least three points - and we're only six games in. A top-drawer goalie will save you 10 points a year, not lose them, and that's why that position is so important.
Lukasz Fabianski deserves credit for his performance in the Champions League in midweek, but you suspect he'll make another mistake soon. One game doesn't make a season and top-drawer goalies will play like that every week.
If Almunia's fit then Arsene Wenger will definitely pick him over Fabianski, but personally I think they need both of them in goal!
As for Chelsea, they had their first real test of the season against Man City last week and they were very disappointing. Having looked so dominant in the first few games they didn't look like scoring a goal at Eastlands.
You have to give credit to City. They got their tactics right and stopped Chelsea playing, but it will be very different on Sunday. Arsenal don't know how to play a containing game like City did.
Arsenal will dominate possession like they have in the last few meetings between these sides. They were outstanding for the first 20-25 minutes at home to Chelsea last year - and then got blown away. They also had more of the ball at Stamford Bridge and got beaten.
Chelsea aren't fussed about letting Arsenal have the ball. They are superb at defending and will allow Arsenal to play in front of them before hitting them.
I think that will be the case again on Sunday. Chelsea are just too powerful and strong for this Arsenal side.
HOME WIN - I'll say 3-1 to Chelsea. They seem to have something over Arsenal at the moment and I think their strength and power will be too much. Both sides looked good in the Champions League this week, but it'll be Chelsea for me on Sunday.
MERSON'S MAGIC MAN
NICOLAS ANELKA - He's a top-drawer player and if he plays well he's capable of ripping people apart. He'll play in a wider position, but will come inside to join Drogba and he's an important part of that Chelsea team. He has proved his class with the fantastic penalties he scored against Newcastle and Marseille.