What you believed almost came to pass but I saw that determination on the faces of the Arsenal players, getting to this stage meant a lot for Arteta and his boys. With how Porto was playing I thought Arsenal was going to be kicked out at extra time but when it got to penalty shootouts that was when I know things are turning out for good for the Arsenal side.
When it comes to penalty shootouts nobody is perfect, even for the goalkeeper too, is a 50/50 thing and the pressure is much on the players not the goalkeepers.
The Porto side were good as hell and I must congratulate them for getting this far and they should also know that between the both teams is Arsenal who have that hunger to be at the next stage after a long while off participating in the Champions League.
I agree with your sentiment here, though fc Porto gave arsenal football club a better fight, but it was arsenal that needed it more, because it wouldn't be pleasant for even the neutral fan for arsenal to let fc Porto eliminate them from this year champions league, because expectations between the both clubs are different, expectations at arsenal is way much higher than that of Porto.
Though I never expected fc Porto to go toe to toe with arsenal at the Emirates stadium, I thought they would be more defensive, just as the first leg, but luck wasn't just on their side yesterday, if not, the result would have been different, but anyway, congratulations to arsenal for progressing to the next stage of the competition.