After three years at Chelsea, Oscar's best game remains his first. On September 19, 2012, Chelsea hosted Juventus, and Roberto di Matteo handed the young Brazilian his first start as a Blue. He was tasked with shutting down Andrea Pirlo, and ended up utterly humiliating the stately midfielder. Juventus had no answer to Oscar that didn't involve kicking him off the pitch; their comeback only really got on its feet after they'd succeeded in injuring him.
And since then he's been ... fine? Good, even. But he's never had a game quite like that first night at Stamford Bridge, when he was both an impossibly disruptive force off the ball and unbridled joy on it. Oscar is a fine player, and one of the keys to Chelsea's game (just watch how ponderous the attack looks without him conducting it), but it's impossible to help feeling like he could be even more than that.
Jose Mourinho knows it and Oscar does as well:
I think I have the quality, I am strong in the mind and good with my feet. If I play my best, I will try to win the Player of the Year. The manager wants me to play like Eden did and at the top level all the season.
Oscar's having his first long break in his entire career as a professional footballer this summer, so there are much higher expectations surrounding him than usual. One gets the feeling that this will be a make-or-break year for him, and if he doesn't come a little closer to living up to his potential he might not be around much longer. But we've already seen what he can do at his best, and if he comes anywhere near that, he'll be at Chelsea for a long, long time.
Whether that actually happens is in his hands now.