The Hammers put up a brave fight in defeat at Manchester United this week.
Demel told the London Evening Standard: "We should take confidence from the way we played at Old Trafford. United were worried near the end of the game and the stadium was quiet - I couldn't hear their fans.
"We're disappointed but the positive thing we must do is take the way we played against United into Saturday's match against Chelsea.
"It wasn't the greatest of starts. We conceded the goal much too early which caused us a problem but the reaction was really good. We also had some chances but couldn't put the ball in the net.
"We're back at home on Saturday and if we play like we did against United and are able to create chances, then I think we have a chance to win the game.
"United are a great team but it wasn't an easy match for them. We had a bad day against Tottenham but every game is different. When you look at the season as a whole so far, I believe we're doing well.
"Now we're at home after the two away games and we will be able to push forward more. We will not hide, we will go for the three points."