The big defender, who returned at the Stadium of Light after missing out at Burnley with an eye injury, felt that the first goal was always likely to determine the outcome of the game and two in quick succession left too steep a hill to climb.
"We knew what to expect really coming here," reflected Dean. "We knew it would be a battle and that they'd pressurise us.
"We worked hard to get in at half-time 0-0 and I think the first goal was always going to be key. We had a great chance, but unfortunately Simon caught it and it went the wrong side of the post.
"We didn't have time to respond before the second one came about, so we never had a chance to recover from the first one.
"We can't dwell on this for too long, it's gone now. We're playing on Saturday and that will come around pretty quickly - we've got to be ready for that."
Despite suffering the eye injury against Chelsea, Dean was sure he would be ready to feature against Sunderland.
"I trained for the first time with a ball on Saturday. I never had any doubt about playing here, I was touch and go on Wednesday.
"It took a layer of skin off the eye brow. It was quite painful and I was struggling in the lights and watching TV - but it's getting better."
Dean Richards insists that the team must not dwell on defeat at Sunderland for too long - with a certain big game looming!