Alberto is riding above expectations. His own, his team, the public. He set his expectations low and is exceeding them so far. His leg and body are responding better than he anticipated. The body because he still had residual Tour form, maybe. The leg is holding up under pressure. IMO no one, including Alberto, Knew In Advance how his leg would handle race pressure.
He always said his form would increase throughout, and that he was lacking explosiveness and race rhythm. Both have been true. His condition is improving. The leg is holding up.
His rivals have not shown any excellence so far. This is key. He attacked yesterday because he saw Froome in difficulty. Two rivals showed they could chase him down. Froome and Valverde lost a bit of time but nothing that will lose them the race if they recover well.
The ITT will tell us much more about where every one is including Alberto. There is a long way to go.