It's true that Spain's normal playstyle is to pass the ball around to sap the other team's stamina and then pounce when they get tired. But this didn't work in the Portugal or Italy match. In fact, Italy had the majority ball possession for a change (at least the first half). Regarding the Portugal match, there was a very clear difference in stamina between Portugal and Spain, in favor of Spain. Portugal was better side the first half, the second half it was tied and only in extra time did Spain suddenly get the upper hand, overpowering Portugal with ease. And Spain has won many a finals match in extra time, so doping would definitely be very useful.
I didn't see Spain superior to Portugal until the extra time. Did you see how brutal the pressing of Portugal was? Spain was suffocated, they couldn't make their usual game, and that way you end up paying at the end of the match. Portugal resisted because of their best physical shape until the extra time, where Spain passed over them and had the best chances of winning before pk's. Portugal didn't measure their effort and wasted all their fuel in the first 75 minutes. Spain is more like a diesel engine.
The Italy possession is easy to explain: Spain scores early, Italy reacts pushing harder (don't forget that the rivals also play, and they play well) making an extra effort to reenter the match as soon as possible, instead of that they receive another goal a counter attack. When you are down 2 goals on a final you are going to do a great physical effort, voluntarily or not, then, when you are left with 10 players, it all comes down like a card castle.