Diame came off the bench to score the second goal in the Hammers' 3-1 win in the reverse fixture on 1 December.
Sam Allardyce's side were not in action this weekend due to the FA Cup but they won their last league match at Stoke 1-0 to give them a further boost.
"It's about confidence, it's 11 v 11 on the pitch whether we're at home or away," Diame told the club's official website.
"I don't know why we haven't got better results when we've played away this season, so the Stoke result was very important for us and now we can look forward to the Chelsea game.
"We have to go there, give our best on the pitch and try to put them in trouble. Winning at Stoke gives us belief and that's important.
"We beat Chelsea at home earlier in the season and it was a very good win. You always want to play when you're up against the big four, so I was happy to get on and play my part. I had a lot of confidence going into that game, and that helped me to do my job on the pitch that day.
"Emotionally, that was the best feeling I've had at West Ham. The fans were very happy and pushed the team on when Coley scored the equaliser. It was a great atmosphere and it got even better when we scored the second and third to win the game.
"Now Chelsea know what we can do, so it's not going to be easy, but we just need to give our best and we'll see what happens.
"They have good players there, but we will have our chance too. We know how we want to play and we're going to prepare well over the week, watch videos of Chelsea to see how they've played in recent games and then try to stop them on the day."