The Brazil international played over 60 games for the Blues last season but was often moved around and found himself out wide for large periods.
Now Oscar, 22, has found Mourinho prefers him to play centrally and he is enjoying the position.
"Last year I spent a lot of time on the wing," he told chelseafc.com
"This season, although I have played out wide, I've mainly been used in the middle. It gives me a bit more freedom to express myself but I know how to play in all those positions and I'm very happy with how it's going so far."
An injury-time Eden Hazard penalty earned Chelsea a 2-2 draw at home to West Brom on Saturday and Oscar is pleased with the start the Blues have made at Stamford Bridge.
"We have been very strong at home and, of course, we need to be if we want to win the title and do well in the cup competitions," he added.
"If you win all the games at home that's the most important thing.
"We have almost qualified for the next round in the Champions League and we've been very good in the Premier League. If we can win all our games at home and try to find a way of picking up points away we will do well."