Chelsea have enough brilliant attacking players that they are never truly out of any game. Their band of three attacking midfielders behind Fernando Torres is one of the most talented in the world, and there's no reason to believe they're not capable of pulling two goals out of absolutely nowhere at any given time.
However, they don't look like coming back against Manchester United at this point in time, which is incredible given that they're at home and United's midfield is quite average. The Blues should be able to create chances and dominate possession if they can ever get the ball to Oscar, Eden Hazard and Juan Mata, but they're currently getting steamrolled. United look much more likely to score again than Chelsea do to make this game interesting.
At this point, getting to halftime down 2-0 would be a decent accomplishment for the Blues. They don't look like scoring and need to make adjustments before this game gets out of hand. Through 30 minutes, they've shown very little.