I believe the reasons why we lost the match was because of our poor defending. Taking off Arbeloa to bring in Babel was not the right decision, nor does taking off Mascherano to bring in Riera made any sense.
If I was in Rafa's shoes, I would've brought in Riera in place of Benayoun on the hour mark and wait to see if I needed another attacker. If so, I would push then Kuyt alongside Torres, and I'd bring Babel to play on the right wing with atleast 20 minutes to go.
Mascherano and Alonso, with our back 4 would have been enough to stop Chelsea from scoring the last two goals. their first two goals were flukes and we could've won the match if Reina did better.
all in all, we played a very good game, and now we should focus on the Premiership which is not far off. a win against Arsenal COULD MEAN that we will win the league!
if we:
1. win all of our matches
2. Man utd draw in two matches
3. maintain the goal difference
then we will win it !