The Baggies remain in trouble after only one victory in 10 games in all competitions.
Di Matteo said: "We just need a win to get ourselves going again. We need to stay positive that we can do that. There are a lot of clubs involved, it is very tight.
"We need to show togetherness, fight for the cause and not forget what our strength is."
Di Matteo added: "I am disappointed with the way the goals came about, especially the two penalties because there wasn't any danger there. So you give them two goals when it is difficult enough facing City.
"But we said at half-time if we didn't concede one and scored one then we could get back in the game. The second half was much better."