That's what happens when you get pressured all game. It messes with your head and you miss open shots. Honestly he was due for this to happen to him. Nobody has ever played as on fire as he has and OKC has flat out got into his head now.
Yeah, it was quite visible yesterday how he was very nervous and without his classic rhythm. For example: when he missed the second free throw (2nd quarter, I think?), just look at how he shoots the one that followed, it wasn't his usual style of shooting. Or better, it wasn't as confident and fluid as usual. Probably the posterchild of how OKC got him under his skin is the third quarter: I don't remember the exact time, but he started to make baffling assist attempts, which became turnovers for GS and great chances for OKC. It's clear how he was pissed as fuck that he couldn't find his rhythm, that OKC's defense was going hard on him, following quite well his movements...those passes were the representations of him trying to catch his rhtym again quickly, before Oklahoma City could escape again. While the injuries he suffered probably are still playing a role right now, I'd dare to say it's minor compared to whatever is going on in his mind now, thanks to OKCs's defense.
Still, it's ridiculous to call him a fraud. What he did during the Regular Season is among some of the most insane moments of basketball in recent times, crazyness at the highest levels, and it's not just the shooting: think about his handling (which plays a major role in the shots he takes), the movements on the field, the energy that brings to the whole team. His rhythm (again) was almost unstoppable in RS, you can't call him a bad player, a fraud, one who's just been lucky...you aren't just the result of pure luck for months over months over months. The same for Golden State as a whole. 73-9 is a legendary Regular Season. Unfortunately, it's also true that, right now, tomorrow is their last chance to make the Western Conference Finals to go on, and I don't know if this OKC wants to stop the magic right now. No, definitely they don't.
P.S. When did Steven Adams become this reliable at the free throw line, quite shocked by that.