Simple, both teams want to win, because both teams need points.
Portsmouth will not fold just yet, they grabbed some much-needed points over the weekend, and will want to do their best to obtain something today vs. Chelsea, because relegation is near.
Chelsea recently got knocked out of the Champions League by Inter, as we all know, so their main focus now is the Premier League. We all know Chelsea can score, and especially now that they don't have to focus on CL, I expect them to come out gunz blazing.
The only thing that worries me about this going over is the return of GK Cech.
Chelsea should be able to drop at least 3 in Portsmouth' net, and Port should be good for at least 1.