The 23-year-old was one of several players to impress as the Blues ended City's 100 per cent home record, and Mourinho believes the Belgian attacker, in time, can emulate Lionel Messi and Cristiano Ronaldo.
|3/4||Chelsea are 3/4 with Betway to score in both halves v Newcastle|
"Give him time, and Willian, [Andre] Schurrle, [Mohamed] Salah too. Give them time. They need good results and so this result is very important for them."
Mourinho believes his side are still evolving and learning, with Monday's victory over City an important lesson in their development, but suggested his side remain the underdogs in the race for the title.
"We are a team in evolution but this is the kind of performance that helps the team to grow up a lot. Tactically and mentally I think it was fantastic," continued the former Real Madrid boss.
"A victory is a victory but a victory against a very good team is better than against an ordinary team. This is also good for the Champions League because we have big opponents so this is a good feeling and a good experience. Today was special.
"We love the big games. When you love it maybe you feel extra-motivated. The best thing for our evolution is to play matches under pressure, to be close to the leaders, and today we came here and played against the leaders and we deserved it.
"There are two horses and a little horse - a little horse that still needs milk and work and to learn how to jump. There are two big horses and the last horse, a horse that next season can race.
"We have beaten the best team twice. In the first game we won because Fernando [Torres] was bright; now we won because we were the best team."